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Show 370 PINGUICULA VULGARIS. CHAP. XVI. these leaves were sent me, each having caught on an average 2·4 inRects. To nine of them, leaves (mostly of Hrica tetralix) adhered; but they had been specially selected on this latter account. I may add that early in August my son found leaves of this same Edca and the fruits of a Carex on the leaves of a Pinguicula in Switzerlancl, probably Pinguicula alpina; some insects, but no great number, also adhered to the leaves of this plant, which had much better developed roots than thoRo of Pinguir:ula 'VI tlyan:.". In Cumberland, Mr. Marshall, on September 3, carefully examined for me ten plants bearing eighty leaves; and on sixtythree of these (i.e. on 79 per cent.) he found insectR, 143 in number; so that each leaf had on an average 2·27 insectR. A few days later he sent me some plants with Bixteen seeds or fruits adhering 1o fourteen leaves. There was a seed on three leaves on the . arne plant. The sixteen seeds belonged to nine different kinds, which could not be reeognisPd, excepting ono of Ranunculus, and several belonging to three or four distinct Bpecies of C.arex. It appears that fewer insects are caught late in the year than earlier ; thus in Cum berland from twenty to twenty-four insects were observed in the middle of July on several leavcR, whereas in the beginning of September tho averao·e num her was only 2·27. Most of the insects, in all tho foregoing caf;cs, were Diptera, but with many minute Hymenoptera, including some ants, a few small Coleoptera, larvm, spiders, and even small moths. vVe thus see that numerous insects and other objects are caught by th viscicll aves; but we have no right to infer from this fact that the habit is beneficial to the plant, any more than in the before given case of the Mirabilis, or of the horse-chestnut. But it will presently be seen that dead insects and other nitrogenous bodies excite the glands to increased secretion ; and that the secretion then becon1es acid and has the power of digesting animal substances, such as albumen, fibrin, &c. Moreover, the dissolved nitrogenous matter is absorbed by the glands, as shown by their limpid ~ontents being aggregated into slowly n1oving granular masses of protoplasm. The same results follow , when insects are naturally captured, and as the plant lives in poor soil and has s1nall roots, there can be no CHAP. XVI. MOVEMENTS OF THE LEAVES. 371 doubt that it profits by its pow r of digesting and absorbing matter from the prey which it habitually aptures in such large numbers. It will, however, b onvenient :first to describe the movements of the 1 av s. .1..Yovements oftheLeaves.-That such thick, large leave as those of Pinguicula vulgaris should have the power of curving inwards when excited has never even been suspected. It is necessary to select for experiment leaves with their glands secreting freely, and which have been prevented. from capturing many insects; as old leaves, at least those growing in a state of nature, have , their margins already curled so 1nuch inwards that they exhibit little power of movement, or move very slowly. I will first give in detail the more important experiments which were tried, and then 1nake some concluding remarks. Experimf'nt I.-A young and almost upright leaf was selected, with its two lateral edges equally and very slightly incurved. A row of small flies was placed along one margin. When looked at next day, after 15 Ill's., this margin, but not the other, was found folded inwards, like the helix of the human ear, to the breadth of 1~ of an inch, so as to lie partly over the row of flies (fig. 15). The glands on which the fljes rested, as well as those on the overlapping margin which had been brought into contact with the flies, were all secreting copiously . Fro. 15. . l!.'xpr::rirnent 2.-A row of flies was placed on one margin of a rather old leaf, which lay flat on the ground; and in this ca8c the margin, after the same interval as before, namely 15 hrs., had only just begun (J>ingw:cula vulga1·is.) to curl inwards; but so much secretion Outline of leaf with left had been poured forth that the spoon- margin inflected over ~\ shaped tip of the leaf was filled with it. row of small flies. Experiment 3.-Fragments of a large fly were placed close to the apex of a vigorous leaf, as well as along half one margin. - 2 B 2 |