256 DION^A MUSCIPULA. [Chap. XIII. 



distance in a line at right angles to the midrib, and then 

 have radiated forth on all sides over both lobes. These sev- 

 eral cases prove that the motor impulse travels, in all direc- 

 tions through the cellular tissue, independently of the course 

 of the vessels. 



With Drosera we have seen that the motor impulse is 

 transmitted in like manner in all directions through the 

 cellular tissue; but that its rate is largely governed by the 

 length of the cells and the direction of their longer axes. 

 Thin sections of a leaf of Dionaea were made by my son, 

 and the cells, both these of the central and of the more super- 

 ficial layers, were found much elongated, with their longer 

 axes directed towards the midrib; and it is in this direction 

 that the motor impulse must be sent with great rapidity 

 from one lobe to the other, as both close simultaneously. 

 The central parenchymatous cells are larger, more closely aV 

 tached together, and have more delicate walls than the more 

 superficial cells. A thick mass of cellular tissue forms the 

 upper surface of the midrib over the great central bundle of 

 vessels. 



When the filaments were roughly touched, at the bases of 

 which slits had been made, either on both sides or on one 

 side, parallel to the midrib or at right angles to it, the two 

 lobes, or only one, moved. In one of these cases, the lobe 

 on the side which bore the filament that was touched moved, 

 but in three other cases the opposite lobe alone moved: so 

 that an injury which was sufficient to prevent a lobe moving 

 did not prevent the transmission from it of a stimulus which 

 excited the opposite lobe to move. We thus learn that, al- 

 though normally both lobes move together, each has the 

 power of independent movement. A case, indeed, has al- 

 ready been given of a torpid leaf that had lately re-opened 

 after catching an insect, of which one lobe alone moved when 

 irritated. Moreover, one end of the same lobe can close 

 and re-expand, independently of the other end, as was seen 

 in some of the foregoing experiments. 



When the lobes, which are rather thick, close, no trace of 

 wrinkling can be seen on any part of their upper surfaces. 

 It appears therefore that the cells must contract. The chief 

 seat of the movement is evidently in the thick mass of cells 

 which overlies the central bundle of vessels in the midrib. 



