CHAP. III. THE PROCESS OF AGGREGATION. 59 



influence which induces aggregation should bo trans- 

 mitted at the proper rate from cell to cell. A plant, 

 with its roots in water, was left for 45 m. in a vessel 

 containing 122 oz. of carbonic acid. A leaf from this 

 plant, and, for comparison, one from a fresh plant, were 

 both immersed for 1 hr. in a rather strong solution 

 of carbonate of ammonia. They were then compared, 

 and certainly there was much less aggregation in the 

 leaf which had been subjected to the carbonic acid 

 than in the other. Another plant was exposed in 

 the same vessel for 2 hrs. to carbonic acid, and one of 

 its leaves was then placed in a solution of one part of 

 the carbonate to 437 of water; the glands were in- 

 stantly blackened, showing that they had absorbed, 

 and that their contents were aggregated; but in the 

 cells close beneath the glands there was no aggre- 

 gation even after an interval of 3 hrs. After 4 hrs. 

 15 m. a few minute spheres of protoplasm were formed 

 in these cells, but even after 5 hrs. 30 m. the aggre- 

 gation did not extend down the pedicels for a length 

 equal to that of the glands. After numberless trials 

 with fresh leaves immersed in a solution of this 

 strength, I have never seen the aggregating action 

 transmitted at nearly so slow a rate. Another plant 

 was left for 2 hrs. in carbonic acid, but was then 

 exposed for 20 m. to the open air, during which time 

 the leaves, being of a red colour, would have absorbed 

 some oxygen. One of them, as well as a fresh leaf 

 for comparison, were -now immersed in the same solu- 

 tion as before. The former were looked at repeatedly, 

 and after an interval of 65 m. a few spheres of 

 protoplasm were first observed in the cells close be- 

 neath the glands, but only in two or three of the 

 longer tentacles. After 3 hrs. the aggregation had 

 travelled down the pedicels of a few of the tentacles 



