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Show 384 PINGUICULA VULGARIS. CHAP. XVI. acid secretion, but were not quite dissolved afte~· two days; and the glands then began to dry. Nor could thmr complete dissolution have been expected from what we have seen with Drosera. (11) Minute drops of skimmed mille were placed on a leaf, and these caused the glands to secrete freely. After 3 hrs. the milk was found curdled, and after 23 hrs. the curds were dissolved. On placing the now clear drops un~er the micros~ope, nothing could be detected except some oil-globules. T.lle secretion therefore, dissolves fresh casein. ' (12) Two fragments of a leaf were immersed for 17 hrs., each in a drachm of a solution of carbonate cif ammonia, of two strengths, namely of one part to 437 and 218 of water. The glands of the longer and shorter hairs were then examined, anrl their contents found aggregated into granular matter of a brownish-green colour. These granular masses were seen by my son slowly to change their forms, and no doubt consisted of protoplasm. The aggregation was more strongly pronounced, and the movements of the protopla~m more rapid, within the glands subjected to the stronger solution than in the others. The experiment was repeated with the same result; and on this occasion I observed that the protoplasm had shrunk a little from the walls of the single elongated cells forming tho pedicels. In order to observe the process of aggregation, a narrow strip of leaf was laid edgeways under the microscope, and the glands were seen' to be quite transparent; a little of the stronger solution (viz. one part to 218 of water) was now added under the covering glass ; after an hour or two the glands contained very fine granular matter, which slowly became coarsely granular and slightly opaque; but even after 5 hrs. not as yet of a brownish tint. By this time a few rather large, transparent, globular masses appeared within the upper ends of the pedicels, and the protoplasm lining their walls had shrunk a little. It is thus evident that the glands of Pinguicula absorb carbonate of ammonia; but they do not absorb it, or are not acted on by it, nearly so quickly as those of Drosera. (13) Little masses of the orange-coloured pollen of the common pea, placed on several leaves, excited the glands to secrete freely. Even a very few grains which accidentally fell on a single gland caused the drop surrounding it to increase so much in size, in 23 hrs., as to be manifestly larger than the drops on the adjoining glands. Grains subjected to the secretion for 48 hrs. did not emit their tubes; they were quite discoloured, and seemed to contain less matter than before; that CHAP. XVI. SECRETION, ABSORPTION, DIGESTION. 385 which was le~t being _of a dirty colour, including globules of oil They thus d1ffered In appearance from other · k t · · water for the same length of time The glancls I?nTamst etp .t1 . . · ' con ac WI ln 1 the pollen-grmns _had evidently absorbed matter from them; for they had lost the1r natural pale-green tint' and cont ai·n e d ao·o-re-gated globular masses of protoplasm. bb (~4) t;quare hits o~ the leaves of spinach, ca,bbage, and a saxifrage, ~nd the entire l_eaves of Erica tetl'alix, all excited the g.lands to _Increased secretiOn. The spinach wn.s the most effective, for It caused the secretion evidently to increase in 1 1· 40 m., and ultimately to run some way down the leaf . but t~r. glands soon began to dry, viz. after 35 hrs. The leave~ of E · e t etra lt' ~ b egan t o. act I.n ! hrs. 30 m., but never caused munccha t she?retiOn t; hnor 1 d1dd the b_Its of leaf of the saxifrage, though in IS case ~ g a_n s contmued to secrete for seven days. Some leaves of Pinguicula were sent me from North Wales to wh' h leaves of E~ica tetrulix an~ of an unknown plant adh~red; a~d the glands In .contact with th~m had their contents plainly aggregated, as If they had been In contact with insects; whilst the other glands on the same leaves contained only clear homogeneous fluid. (15) Seeds.-A considerable number of seeds or fruits se .. lected by hazard, some fresh and some a year old some soaked for a short. time _in water and some not soaked, we;e tried. The ten following kmds, namely cabbage, radish, Anemone nemoror.; a, Rumex ace_tosa, Garex sylvatica, mustard, turnip, cress, Bununculus acns, and Avena lJubescens, all excited much secretion, which was in several cases tested and found always acid. The five first-named seeds excited the glands more than the others. The secretion was seldom copious until about 24 hrs. had elapsed, no doubt owing to the coats of the seeds not beino· easi'1 y permeable. Nevertheless, cabbage seeds excited someb secretion in 4 hrs. 30 m. ; and this increased so much in 18 hrs. as to run down the leaves. The seeds or properly the fruits of Carex are much oftener found adhering to leaves in a state of nature than those of any other genus; and the fruits of Garex sylvatica excited so much secretion that in 15 hrs. it ran into the incurved edges; but the glands ceased to secrete after 40 hrs. On the other hand, the glands on which the seeds of the Rumex and Avena rested continued to secrete for nine days. The nine follo:ving kinds of seeds excited only a slight amount of secretiOn, namely celery, parsnip, caraway, L1:num grandijlorum, Cassia, Trifvlt'um pannouicum, Plantago, onion, 2 c |
