216 DROSERA ROTUNDIFOLIA. [Chap. XI. 



mit centrifugally an influence up the pedicels of the ex- 

 terior tentacles to their glands; but the actual process of 

 aggregation travels centripetally, from the glands of the 

 exterior tentacles down their pedicels. The exciting in- 

 fluence,' therefore, which is transmitted from one part of 

 the leaf to another must be different from that which actu- 

 ally induces aggregation. The process does not depend on 

 the glands secreting more copiously than they did before; 

 and is independent of the inflection of the tentacles. It 

 continues as long as the tentacles remain inflected, and as 

 soon as these are fully re-expanded, the little masses of pro- 

 toplasm are all redissolved; the cells becoming filled with 

 homogeneous purple fluid, as they were before the leaf was 

 excited. 



As the process of aggregation can be excited by a few 

 touches, or by the pressure of insoluble particles, it is evi- 

 dently independent of the absorption of any matter, and 

 must be of a molecular nature. Even when caused by the 

 absorption of the carbonate or other salt of ammonia, or an 

 infusion of meat, the process seems to be of exactly the same 

 nature. The protoplasmic fluid must, therefore, be in a 

 singularly unstable condition, to be acted on by such slight 

 and varied causes. Physiologists believe that when a nerve 

 is touched, and it transmits an influence to other parts of 

 the nervous system, a molecular change is induced in it, 

 though not visible to us. Therefore it is a very interesting 

 spectacle to watch the effects on the cells of a gland, of the 

 pressure of a bit of hair, weighing only rrhnr of a grain 

 and largely supported by the dense secretion, for this ex- 

 cessively slight pressure soon causes a visible change in the 

 protoplasm, which change is transmitted down the whole 

 length of the tentacle, giving it at last a mottled appear* 

 ance, distinguishable even by the naked eye. 



In the fourth chapter it was shown that leaves placed for 

 a short time in water at a temperature of 110 Fahr. (43'*.3 

 Cent.) become somewhat inflected; they are thus also ren- 

 dered more sensitive to the action of meat than they were 

 before. If exposed to a temperature of between 115** and 

 125* (46**.l Sl^.e Cent.), they are quickly inflected, and 

 their protoplasm undergoes aggregation; when afterwards 

 placed in cold water, they re-expand. Exposed to 130* 



