38G TINGUICULA VULGARIS. CHAP. X VI 



and Bromus. Most of these seeds did not excite any secretion 

 until 48 hrs. had elapsed, and in the case 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, Erica tetral/\r, Atriplex hortensis, 

 P /talaris canariensis, and wheat. Nevertheless, when the seeds 

 of the lettuce, wheat, and Atriplex were split open and applied 

 to leaves, secretion was excited in considerable quantity in 

 10 hrs., and I believe that some was excited in six hours. In 

 the case of the Atriplex the secretion 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 secretion, and only after a 

 long interval of time. A slice of the common pea, which how- 

 ever was not tried whole, caused secretion in 2 hrs. From 

 these facts we may conclude that the great difference in tho 

 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 pre- 

 viously 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 appa- 

 rently 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 sur- 

 rounding 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 ihem being killed, or by the seedlings being injured. Fourteen 

 cabbage seeds were left for three days on leaves and excited 



