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Show 386 PINGUICULA VULGARIS. CHAP. XVI. and Bromus. Most of these seeds did not excite any secretion until 4B hrs. had elapsed, and in tho cas~ of the Trifolium only one seed acted and this not until the third day. Although the seeds of the Plantago excited very little secretion, the glands continued to secrete for six days. Lastly, the five following kinds excited no secretion, though left on the leaves for two or three days, namely lettuce, b'r-ica tetr-alb.;, Atn"plex hortr:nsis, Phalaris canariens£s, and wheat. Nevertheless, when tho seeds of the lettuce, wheat, and Atriplex were split open and applied to leaves secretion was excited in considerable quantity in 10 brs. a~d I believe that some was excited in six hours. In the cas~ of the Atriplex the secretion ran down to tho margin, and after 24 hrs. I speak of it in my notes "as immense 'in quantity and acid." The split seeds also of the Trifolium and celery acted powerfully and quickly, though the whole seeds caused as we have seen, very little secretion, and only after a long i~terval of time. A slice of the com:non. pea, which however was not tried whole, caused secretiOn In 2 hrs. From these facts we may conclude that the great difference in the degree and rate at which various kinds of seeds excite secretion, is chiefly or wholly due to the different permeability of their coats. Some thin slices of the common pea, which had been previously soaked for 1 hr. in water, were placed on a leaf, and quickly excited much acid secretion. A~ter 24 hrs. ~h~se slices were compared under a high power With others left m water for the same time · the latter contained so many fine granules of legumin that the slide was rendered muddy; whereas the slices which had been subjected to the secretion were much cleaner and more transparent) the granules of legumin apparently having been dissolved. A cabbage seed which had lain for two days dn a leaf and bad excited much acid secretion, was cut into slices, and these were compared with those of a seed which had been left for the same time in water. Those subjected to the secretion were. of a paler colour; their c~ats presenting the greatest differences, for thBy were of a pa.Ie duty tint instead of chestnut-brown. The glands on whiCh the cahbage seeds had rested, as well as those bathed by the surrounding secretion, differed greatly in appearance from the other glands on the same leaf, for they all contained brownish granular matter, proving that they had absorbed matter from the seeds. That the secretion acts on the seeds was also shown by some of them being killed, or by the seedlings being injured. Four~een cabbage seeds were left for three days on leaves and exCited CnAP. XVI. SECRETION, ABSORPTION, DIGESTION. 3 7 much secretion; they were then placed on damp and under conditions known to be favourable for germination. Three never germinated, and this was a far larger proportion of deaths than occurred with seeds of the same lot, which bad not been subjected to the secretion, but were otherwise treated in the same manner. Of the eleven seedlings raised, throe had the edges of their cotyledons slightly browned, as if scorched; and the cotyledons of one grew into~ curious indented shape. Two mustard seeds germinated; but their cotyledons were marked with brown patches and their radicles deformed. Of two ra lish seeds, neither germinated; whereas of many seeds of the same lot not subjected to the secretion, all, excepting one, germinated. Of the two Rumex seeds, one died and tho other germinated; but its radicle was hrown and soon withered. Both seeds of the Avena germinated, nne grew well, the other had its radicle brown and withered. Of Rix seeds of the Erica none germinated, and when cut open after having been loft for five months on damp sand, one alone seemed alive. Twenty-two seeds of various kinds were found adhering to the leaves of plants growing in a state of nature; and of these) though kept for five months on damp sand, none germinated, some being then evidently dead. The Eff~ets of Ohjects not containing Soluble }..T-itrogenous Matter. (16) It has already been shown that bits of glass, placed on leaves, excite little or no secretion. rrhe small amount which lay beneath the fragments was tested and found not acid. A bit of wood excited no secretion; nor did the several kinds of seeds of which the coats are not permeable to the secretion, and which, therefore, acted like inorganic bodies. Cubes of fat, left for two days on a leaf, produced no effect. (17) A particle of white sttgar, placed on a leaf, formed in 1 hr. 10 rn. a large drop of fluid, which in the course of 2 additional honrs ran down into the naturally inflected margin. This fluid was not in the least acid, and began to dry up, m· more probably was absorbed, in 5 hrs. 30m. The experiment was repeated; particles being placed on a leaf, and others of the same size on a slip of glass in a moistened state; bot.h being covered by a bell-glass. This was done to see whether the increased amount of fluid on the leaves could be due to mere deliquescence; but this was proved not to be the case. The particle on the leaf caused so much secretion that in the course of 4 hrs. it ran down across two-thirds of the leaf. After B hrs. the leaf, which was concave, was actually filled with very viseicl 2 c 2 |