Chap. XVI.] SECRETION, ABSORPTION, DIGESTION, 313 



some were excited in six hours. In the case of the Atriplex the se- 

 cretion ran down to the 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 secre- 

 tion, and only after a long interval of time. A slice of the com- 

 mon 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 secre- 

 tion, 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 ex- 

 cited much acid secretion. After 24 hrs. these slices were com- 

 pared 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 was much cleaner and more trans- 

 parent, 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 injuretl. Fourteen 

 cabbage seeds were left for three days on leaves and excited nwich 

 secretion; they were then placed on damp sand under conditions 

 known to be favourable for germination. Three never germinated, 

 and this was a &ir larger proportion of deaths than occurred with 

 seeds of the same lot, which had not been subjected to the secre- 

 tion, 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 cotyle<lons were marked with brown patches and their radi- 

 cles 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 dietl 

 and the other germinated ; but its radicle was brown and soon 

 withered. Both seeds of the Avena germinate<l, 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 



