54 DROSERA ROTUNDIPOLU. [Chap. III. 



That the central glands, if irritated, send centrifugally 

 some influence to the exterior glands, causing them to send 

 back a centripetal influence inducing aggregation, is per- 

 haps the most interesting fact given in this cnapter. But 

 the whole process of aggregation is in itself a striking phe- 

 uomenon. Whenever the peripheral extremity of a nerve is 

 touched or pressed, and a sensation is felt, it is believed that 

 an invisible molecular change is sent from one end of the 

 nerve to the other; but when a gland of Drosera is re- 

 peatedly touched or gently pressed, we can actually see a 

 molecular change proceeding from the gland down the tenta- 

 cle ; though this change is probably of a very different nature 

 from that in a nerve. Finally, as so many and such widely 

 different causes excite aggregation, it would appear that 

 the living matter within the gland-cells is in so unstable a 

 condition that almost any disturbance suffices to change its 

 molecular nature, as in the case of certain chemical com- 

 pounds. And this change in the glands, whether excited 

 directly, or indirectly by a stimulus received from other 

 glands, is transmitted from cell to cell, causing granules of 

 protoplasm either to be actually generated in the previously 

 limpid fluid or to coalesce and thus to become visible. 



Supplementary Observations on the Process of 

 Aggregation in the Roots of Plants. 



It will hereafter be seen that a weak solution of the carbonate 

 of ammonia induces aggregation in the cells of the roots of 

 Drosera; and this led me to make a few trials on the roots of 

 other plants. I dug up in the latter part of October the first 

 weed which I met with, viz. Euphorbia peplua, being careful not 

 to injure the roots; these were washed and placed in a little solu- 

 tion of one part of carbonate of ammonia to 146 of water. In less 

 than one minute I saw a cloud travelling from cell to cell up the 

 roots, with wonderful rapidity. After from 8 m. to 9 m. the fine 

 granules, which caused this cloudy appearance, became aggregated 

 towards the extremities of the roots into quadranf;ular masses of 



Sown matter; and some of these soon changed their forms and 

 came spherical. Some of the cells, however, remained unaffected. 

 I repeated the experiment with another plant of the same species, 

 but before I could get the specimen into focus under the micro- 

 scope, clouds of granules and quadrangular masses of reddish and 

 brown matter were formed, and had run far up all the roots. A 

 fresh root was now left for 18 hrs. in a drachm of a solution of 

 one part of the carbonate to 437 of water, so that it received i of 



