224 DROSERA ROTUNDIFOLU. [Cu ap. \ I. 



cepted, as these do not bend at all when thus excited. On 

 the other hand, when the motor impulse comes from one 

 side of the disc, the surrounding tentacles, including the 

 short ones in the middle of the disc, all bend with precision 

 towards the i}oint of excitement, wherever this may be 

 seated. Thj^ is in every way a remarkable phenomenon ; for 

 the leaf falsely appears as if endowed with the senses of an 

 animal. It is all the more remarkable, as when the motor 

 impulse strikes the base of a tentacle obliquely with respect 

 to its flattened surface, the contraction of the cells must 

 be confined to one, two, or a very few rows at one end. And 

 diflFerent sides of the surrounding tentacles must be acted on, 

 in order that all should bend with precision to the point of 

 excitement. 



The motor impulse, as it spreads from one or more glands 

 across the disc, enters the bases of the surrounding tentacles, 

 and immediately acts on the bending place. It does not in 

 the first place proceed up the tentacles to the glands, exciting 

 them to reflect back an impulse to their bases. Nevertheless, 

 some influence is sent up to the glands, as their secretion is 

 soon increased and rendered acid ; and then the glands, be- 

 ing thus excited, send back some other influence (not de- 

 pendent on increased secretion, nor on the inflection of the 

 tentacles), causing the protoplasm to aggregate in cell be- 

 neath cell. This may be called a reflex action, though prob- 

 ably very diflFerent from that proceeding from the nerve- 

 ganglion of an animal; and it is the only known case of 

 reflex action in the vegetable kingdom. 



About the mechanism of the movements and the nature 

 of the motor impulse we know very little. During the act 

 of inflection fluid certainly travels from one part to another 

 of the tentacles. But the hypothesis which agrees best with 

 the observed facts is that the motor impulse is allied in na- 

 ture to the aggregating process; and that this causes the 

 molecules of the cell-walls to approach each other, in the 

 same manner as do the molecules of the protoplasm within 

 the cells; so that the cell-walls contract. But some strong 

 objections may be urged against this view. The re-ex- 

 pansion of the tentacles is largely due to the elasticity of 

 their outer cells, which comes into play as soon as those 

 on the inner side cease contracting with prepotent force ; but 



