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. 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
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