Page images
PDF
EPUB

of 1 ft. or more. Mr. Lewin thinks the caterpillar generally confines itself to the pith in the centre of the stem; but Mr. Bree finds the pith sometimes untouched, all the perforations being made in the solid wood between the pith and the bark. Being an internal feeder, the caterpillar, of course, is only to be found by cutting into and opening the stems of the willow in which it is enclosed. When the periodical falls of underwood take place, Mr. Bree has observed that scarcely a single willow wand is cut down that does not exhibit proofs of the ravages of this insect; sometimes three or four, or even five, separate perforations occurring in the same stem. Though the Trochílium crabronifórme is a common species, Mr. Bree has never met with an example of the winged insect at large in his neighbourhood (Allesley, near Coventry). He has bred it from the caterpillar; and once he took a single pair in an osier bed near Dudley, which, at the time, were considered as great rarities. "The wood of Salix càprea is, in Warwickshire, usually either sold to the rake-maker, for the purpose of being worked up into rake-teeth, &c.; or converted into what are called flakes, i. e. hurdles made of split stuff nailed together, in contradistinction to the common wicker hurdle, which is formed of round wood, twisted and plaited together without the help of nails. The lower, and consequently the thicker, portion of each willow rod, to

[graphic][merged small]

the length of 5 in. or 6 in., or occasionally I ft. or more, is spoiled by the perforations of the larva, and rendered unavailable to the above purposes." (Mag. Nat. Hist., new se

ries, vol. i. p. 19.) Of the Trochílium crabronifórme (or, more properly T. bembecifórme) a beautiful figure is given by Mr. Curtis in the British Entomology, pl. 372. fig. sup.; and several additional particulars relative to its habits are given by Mr. Westwood, in an article in the third part of the Transactions of the Entomological Society.

[graphic]

a

The caterpillars of Nématus càpreæ feed on the leaves of the sallow (S. cà

prea L.), and of several

species of willow and osier,

1292

to which they are said to be sometimes very destructive.

A cultivator

in the neighbourhood of Penzance, after thoroughly preparing a piece of

moist ground, highly favourable in itself for the growth of osiers, planted it ; and, after a few years, the osiers had disappeared, he hardly knew how. It was planted a second and even a third time, and the plants always disappeared. "My attention," says the writer, "being now strongly drawn to the subject, I discovered that which I ought to have perceived half a century sooner; namely, that Nématus càpreæ, favoured by the peculiar locality, was the cause of all this devastation. The spot is low, moist, shut in by wood, and very near the southern limit of England. The species of willow planted was chiefly one of those with broad leaves, woolly underneath (probably S. càprea L.). The warmth of the situation, and the nidus for eggs afforded by these woolly leaves, were, I presume, the combined cause of the insect being so remarkably attracted to this spot. Some of the plants were of a species with smooth narrow leaves (probably S. triándra L.): these escaped much longer than the others, but still they did not escape eventually, as they were also attacked by another caterpillar. I introduced both red and black ants, and put some of the caterpillars into their nests; but the ants disregarded them altogether. Having, although thus slowly, ascertained the true state of things, the ground was once more cultivated, and was planted with apple trees. As there happens to be no insect there which much attacks these, they thrive very well. The distance at which apple trees are planted is, also, less favourable to the propagation of vermin. I have communicated all this detail in order to show the importance to individuals of attending to such seemingly trifling matters. Many a plantation, &c., fails in an apparently inexplicable manner. A scientific investigation would, in numerous cases, disclose the truth, and prevent farther loss. Had a person acquainted with entomology been proprietor of this osier ground 50 years since, he would speedily have discovered the truth, and might have saved 2007. or more to himself and his successors." (Mag. Nat. Hist., vii. p. 423.)

The Chrysomela (Phæ`don) vulgatíssima L. is another species which is occasionally injurious to one of the narrow-leaved species of willow. This is a pretty little insect, of a shining blue or green colour, and of an oblong-oval form, about in. in length, which is found, during the winter months, in great profusion under the loose bark of willows, growing in damp localities. It deposits its eggs upon the young leaves; and the larvæ, when hatched, form little associations, feeding together in regular rows, the heads of the second row touching the tails of the first. In this manner they proceed from the base to the extremity of the leaf, which they soon strip of its parenchyma. They then attack the next leaf; and so on, until they are full grown, when they descend into the earth, and assume the pupa state; shortly after which they undergo the change to their last and perfect form.

The leaves of some species of willows are also infested with galls, which are the production, not of a species of Cynípidæ, but of one of the Tenthrednidæ (Nématus intércus Panzer Fauna Ins. Germ., 90. fig. 11.; or the Tenthrèdo sálicis pentandra Villars). The larvæ of this insect, instead of feeding externally upon the leaves of the willow, is enclosed in a gall, upon the substance of which it subsists, and within which it undergoes all its changes. Mr. Westwood's species Nématus gallícola (described by Mr. Stephens, Illust. Brit. Ent., vol. vii. p. 36.), and the Euùra Cynips of Newman (Ent. Mag., No. 18. p. 260.), also reside in galls; whilst the larvæ of Nématus sálicis of Saint Fargeau, and of the N. càpreæ, are external feeders.

Among the Lepidoptera, the caterpillars of nearly all the species of moths belonging to the genus Cerùra (puss and kitten moths) feed upon different species of willow; and also, occasionally, the larva of the buff-tip moth (Pygæ`ra bucéphala Steph.). Brèpha Parthènias (the orange underwing) feeds upon poplars and willows; and Notodónta ziczac (the pebble prominent moth) upon the same: Leiocámpa dictæ `a and L. dictæöìdes (the swallow prominent moths), Ptilodóntes palpina (the pale prominent moth), Gastropacha quercifòlia, &c., occasionally upon willows; and the larva of Orthòsia ùpsilon Steph. beneath the bark of old willows and poplars.

The larvæ of Satúrnia Pavònia minor feed on various species of osier. Lozotæ nia cruciàna, a small but beautiful tortrix, lives on a dwarf mountain Salix. Líparis (Leucòma Steph.) sálicis is, in many years, very abundant on different willows. Several species of the very showy genus of Noctuidæ, Catocàla, also feed, in the larva state, upon several species of Salix. These caterpillars exhibit a very interesting instance of deceptive similarity to the plants on which they feed; their colours being of a pale greyish brown, dotted with black, and the sides of their bodies being furnished with a membranaceous lobe, fringed with short whitish hairs, which are applied close to the surface of the twigs, so that it is very difficult for an unpractised eye to perceive them, or to distinguish them from bundles of lichens. The colours of the fore wings of the perfect insects are also equally deceptive, rendering it quite as difficult to perceive the moths when settled upon the trunks of the trees. The hind wings of these moths are, however, very beautifully coloured, being either red or pale blue, with black bands. Catocala fráxini (the great Clifden nonpareil) feeds, in the larva state, on poplar, ash, &c.; C. núpta L. upon Salix vitellina; and C. elocata Esper (the claim of which to be considered a native species is questionable) upon willows and elms. Our fig. 1293. represents the lastnamed species copied from Curtis's British Entomology, pl. 217.; and the generic

[graphic][subsumed]

details, a to i, are from C, núpta. a, b, parts of the antenna; c, spiral tongue; d, palpus; e, palpus denuded; f, the head; g, one of the ocelli; h, hind leg; i, claws.

Amongst Coleoptera, the principal species which feed on the willow are, Galeruca càpreæ, Pyróchroa rùbens (on the rotten wood, whilst in the larva state), Melasòma pópuli and trémula, Balanìnus salicivorus, and Tachyérges sálicis; and, amongst the Hemiptera, A'phis sálicis L., and Cóccus càpreæ and C. sálicis L.

Some parts of the preceding article have been furnished to us by J. O. Westwood, Esq., by whom the whole has been revised.

The Study of the Species. The genus Salix has been a stumbling block to botanists from the time of Linnæus, who observes that so great are the changes effected on the kinds by soil, situation, and climate, that it is difficult to determine whether many of the differences should constitute species, or varieties only. He recommends rejecting the old names and characters, and describing anew the several species accurately, as seen in their natural places of growth. For this purpose, he gives directions for observing the developement of the buds, the situation of the catkins, the form and other circum

stances of the leaves, the number of stamens, and whether the plants are trees, shrubs, or creepers. With due deference to the opinion thus expressed by the great father of scientific botany, we think that the study of willows, or of any other species of plant, in its native habitat is by no means a good mode for determining what are species, and what are varieties; but rather likely, on account of the great difference of habitats, to increase the number of both; since every difference may be considered specific relatively to the circumstances which produce that difference. It appears to us that it would be a better mode to collect plants of the particular genus to be studied from all the different habitats in which they are to be found, and to cultivate and study them in the same garden, where they would be all subjected to the same exterior influences. What Sir J. E. Smith says on this subject does not appear to us much more satisfactory than the advice of Linnæus. "Willows," he says, "should be particularly studied at three different seasons: the flowering time; the early part of summer, when the young shoots, with their stipules and expanding foliage, are to be observed; and, finally, when the leaves are come to their full size. No botanist, therefore, can be competent to form an opinion about them, unless he resides among the wild ones, for several seasons, or continually observes them in a garden. No hasty traveller over a country, no collector of dried specimens, or compiler of descriptions, can judge of their characters or essential differences. One principle, above all, in this department of botany, and indeed in every other, cannot be too strictly enforced. We should study a species before we decide on its characters, and not lay down rules of definition beforehand. In many plants, the differences of simple or compound, entire, serrated, or jagged, leaves; the presence or absence of stipules; though usually so essential and decisive, make no specific distinction at all. In some tribes or genera, one part affords the best specific character, in others some different part. The distinctions of willows are frequently so very nice, that the greatest observation and experience only can stamp them with due authority." (Eng. Fl., iv. p. 165.) After thirty years' study of every kind of willow that could be procured in any part of Britain, in the garden of Mr. Crowe, where seedlings innumerable sprang up all over the ground, Sir J. E. Smith was not only confirmed in the immutability of his species, amounting to 64, as natives of Britain, but also, that new or hybrid species were not produced by the seeds of species growing together in the same garden. Both these conclusions are alike at variance with those of most other botanists. As the result of this eminent botanist's study of the genus, he has arrayed his 64 species of British willows under three sections, characterised by the margins and surfaces of the leaves; viz. 1. serrated and smooth; 2. entire and smooth; and, 3. surface shaggy, woolly, or silky. Since the time of Sir J. E. Smith, the principal British student of willows is Mr. Borrer; and, in Sir W. J. Hooker's British Flora, this able botanist has arranged the British willows, increased in Sir W. J. Hooker's work to 71 species, under 18 sections. These sections are all natural; and each is characterised by the name of a typical species. This is obviously a very great improvement in the arrangement of this genus, whether these kinds are considered as chiefly species, or chiefly varieties; and to us it appears the best adapted for the present state of our knowledge of willows, till all the known kinds shall have been studied for a number of years in one garden.

Among the Continental botanists, the late Dr. Host of Vienna, and Professor Koch of Erlangen, appear to be the principal students of willows. Dr. Host, in the preface to his Salix, seems disposed to consider the kinds of willow that exhibit the same appearances when under the same circumstances of soil and situation as distinct species; and he has described no fewer than 60 of these as natives of Austria. He admits the extreme difficulty of determining what are species in many cases, from the different localities in which the same species is sometimes found. For example, willows which inhabit low moist situations in valleys flower only in the spring; while those which inhabit mountains do not flower till after the melting of the snow, which sel

dom happens before the beginning of summer. On the other hand, very many sorts, in intermediate localities, are intermediate also in their time of flowering. Hence, the same kind, when it inhabits three different regions, cannot be compared together in the same stage of growth in a living state; and, consequently, three species may, in this way, be made out of one. Dr. Host farther observes, that a great impediment to the determining of what are really species, arises from the sexes of a species often inhabiting localities very distant from each other, and sometimes even different regions; and the beautiful figures which illustrate this author's work, on the supposition that they are faithful portraits, clearly show that the male and female differ very considerably in their foliage and wood, independently altogether of their catkins.

The great master in the genus Salix may be considered Professor Koch, who has done more to advance a knowledge of this genus in his 12mo pamphlet of 69 pages, De Salicibus Europæis Commentatio, published in 1828, than the most voluminous of ancient or modern authors. The preface to this pamphlet is so full of instruction as to the mode of studying this family of plants, that we are confident that our readers will feel obliged to us for presenting to them the following

Abstract of Koch's Preface to his Commentary on the Genus Salix. The author, after noticing the difficulties to be encountered in this genus, and referring to what has been done by Linnæus, Wahlenberg, Willdenow, Smith, and others, notices the 119 species which had been sent to him by Schleicher, as found by that botanist in Switzerland, and thus, as we have before observed (p. 1456.), making the total number of species of Sàlix 254. Of Schleicher's species, he says that he could not find one that truly deserved the name.. They are, he adds, mere variations of species long since known; and, for the most part, different forms of one changeable species, viz., his own S. phylicifòlia. All Schleicher's kinds are enumerated as species in Steudel's Nomenclator; but Koch treats them as spurious, he recognising not more than 50 truly distinct European species.

The manner in which Koch obtained his knowledge of the genus Salix is thus given:-"For a number of years, I observed the willows growing wild in the Palatinate; also those I met with during my travels; and those which I have found, during the space of four years, in the neighbourhood of Erlangen. All the species, or singular forms, which I found growing wild were transferred to the garden; and to these were added kinds sent by my friends Mertens and Zeiher, an addition of no small importance. From the former I received genuine English willows in a living state. The whole collection was afterwards transferred to the Botanic Garden at Erlangen, where, neither care nor expense being spared, it has since been much increased. From M. Otto director of the Botanic Garden at Berlin, I also received a number of kinds. Of dried specimens I have received the whole collection of M. Seringe, from that author himself; and the greater number of the Swedish, French, and English willows, gathered in their native habitats, from Mertens; forming in the whole a greater number of species of this genus than was ever before available by one individual.

"Every genus of plants has certain peculiar features, with which constant observation and repeated examination alone can familiarise us; but there is no genus in which it is so necessary as in that of Salix, to investigate, not only its peculiar characters, but also the growth of the plants, both in a wild and a cultivated state. He who endeavours to characterise a species, either from a dried specimen or from a cultivated plant, is always liable to be deceived in its characters. Hence, amongst all the writers on willows from the time of Linnæus, Wahlenberg alone has clearly described them. He travelled through Lapland, Switzerland, the Carpathian Mountains, and Sweden; examining the kinds of this genus in their native places of growth; and, following in his footsteps, came Seringe, also a most diligent investigator. Taking these authors for my guide, although, in some instances, I have been compelled to differ from them, I here offer a synopsis of the European species of willow. "In arranging this genus, and distributing its species, if we put near together

« PreviousContinue »