Chap. III.] THE PROCESS OP AGGREGATION. 51 



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 car- 

 bonate to 437 of water; the glands were instantly blackened, 

 showing that they had absorbed, and that their contents were 

 aj^gregated; but in the cells close beneath the glands there 

 was no aggregation 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 aggregation did 

 not extend down the pedicels for a length equal to that of 

 the glands. After numberless trials with fresh leaves im- 

 mersed 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 com- 

 parison, were now immersed in the same solution 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 beneath 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 for a 

 length equal to that of the glands. On the other hand, iu 

 the fresh leaf similarly treated, aggregation was plain in 

 many of the tentacles after 15 m.; after 65 m. it had ex- 

 tended down the pedicels for four, five, or more times the 

 length of the glands; and after 3 hrs. the cells of all the 

 tentacles were affected for one-third or one-half of their 

 entire lengths. Hence there can be no doubt that the ex- 

 posure of leaves to carbonic acid either stops for a time the 

 process of aggrregation, or checks the transmission of the 

 proper influence when the glands are subsequently excited 

 by carbonate of ammonia; and this substance acts more 

 promptly and energetically than any other. It is known 

 that the protoplasm of plants exhibits its spontaneous move- 

 ments only as long as it is in an oxygenated condition; 

 and so it is with the white corpuscles of the blood, only 

 as long as they receive oxygen from the red corpus- 

 6 



