254 DION^A MUSCIPULA. [Chap. XII L 



teen there was only one, viz. a dipterous insect, which could 

 readily take flight. Drosera, on the other hand, Uvea chiefly 

 on insects which are good flyers, especially Diptera, caught 

 by the aid of its viscid secretion. But what most concerns 

 us is the size of the ten larger insects. Their average length 

 from head to tail was .256 of an inch, the lobes of the leaves 

 being on an average .53 of an inch in length, so that the in- 

 sects were very nearly half as long as the leaves within which 

 they were enclosed. Only a few of these leaves, therefore, 

 had wasted their powers by capturing small prey, though it 

 is probable that many small insects had crawled over them 

 and been caught, but had then escaped through the bars. 



The Transmission of the Motor Impulse, and means of 

 Movement. It is sufficient to touch any one of the six fila- 

 ments to cause both lobes to close, these becoming at the 

 same time incurved throughout their whole breadth. The 

 stimulus must therefore radiate in all directions from any 

 one filament. It must also be transmitted with much rapid- 

 ity across the leaf, for in all ordinary cases both lobes close 

 simultaneously, as far as the eye can judge. Most physiolo- 

 gists believe that in irritable plants the excitement is trans- 

 mitted along, or in close connection with, the fibro-vascular 

 bundles. In Dionsea, the course of tliese vessels (composed 

 of spiral and ordinary vascular tissue) seems at first sight to 

 favour this belief; for they run up the midrib in a great 

 bundle, sending off small bundles almost at right angles on 

 each side. These bifurcate occasionally as they extend to- 

 wards the margin, and close to the margin small branches 

 from adjoining small vessels unite and enter the marginal 

 spikes. At some of these points of union the vessels form 

 curious loops, like those described under Drosera. A con- 

 tinuous zigzag line of vessels thus runs round the whole cir- 

 cumference of the leaf, and in the midrib all the vessels are 

 in close contact; so that all parts of the leaf seem to bo 

 brought into some degree of communication. Nevertheless, 

 the presence of vessels is not necessary for the transmission 

 of the motor impulse, for it is transmitted from the tips of 

 the sensitive filaments (these being about the iv of an inch 

 in length), into which no vessels enter; and these could not 



(Htlon. nB !f all tholr Intornnl nInntR which Rho cnltlvnted !n 

 pnrts had been partially digested. New Jersey chiefly caught Dip- 

 Mrs. Treat Informs me that the tcra. 



