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.  After 24 hrs. these slices were compared under a high power with others left in 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 on a leaf and had 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 coats presenting the greatest differences, for they were of a pale dirty tint instead of chestnut-brown.  The glands on which the cabbage 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.  Fourteen cabbage seeds were left for three days on leaves and excited [page 387] much secretion; they were then placed on damp sand 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 had not been subjected to the secretion, but were otherwise treated in the same manner.  Of the eleven seedlings raised, three had the edges of their cotyledons slightly browned, as if scorched; and the cotyledons of one grew into a curious indented shape.  Two mustard seeds germinated; but their cotyledons were marked with brown patches and their radicles deformed.  Of two radish 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 the other germinated; but its radicle was brown and soon withered.  Both seeds of the Avena germinated, one grew well, the other had its radicle brown and withered.  Of six seeds of the Erica none germinated, and when cut open after having been left 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 Effects of Objects not containing Soluble Nitrogenous Matter.

(16) It has already been shown that bits of glass, placed on leaves, excite little or no secretion.  The 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.