. XIII. TRANSMISSION OF MOTOR IMPULSE. 



313 



were beetles,* and out of the whole fourteen there 

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

 readily take flight. Drosera, on the other hand, 

 lives 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 insects 

 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 filaments to cause both lobes to close, these becom- 

 ing 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 rapidity across the leaf, for in 

 all ordinary cases both lobes close simultaneously, 

 as far as the eye can judge. Most physiologists be- 

 lieve that in irritable plants the excitement is trans- 

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

 vascular bundles. In Dionoea, the course of these 

 vessels (composed of spiral and ordinary vascular 



* Dr. Canby remarks (' Gar- 

 dener's Monthly,' August 1868), 

 "as a general thing beetles and 

 insects of that kind, though al- 

 ways killed, seem to be too hard- 

 shelled to serve as food, and after 

 a short time are rejected." I am 

 eurprised at this statement, at 

 least with respect to such beetles 



as elaters, for the five which I 

 examined were in an extremely 

 fragile and empty condition, as if 

 all their internal parts had been 

 partially digested. Mrs. Treat 

 informs me that the plants which 

 she cultivated in New Jersej 

 chiefly caught Diptera. 



