SIO DROSERA ROTUNDIFOLIA. [Chap. X. 



the movement can hardly be attributed to the elasticity of 

 the walls, together with a previous state of tension." 



With respect to the nature of the motor impulse which is 

 transmitted from the glands down the pedicels and across 

 the disc, it seems not improbable that it is closely allied to 

 that influence which causes the protoplasm within the cells 

 of the glands and tentacles to aggregate. We have seen that 

 both forces originate in and proceed from the glands within 

 a few seconds of the same time, and are excited by the same 

 causes. The aggregation of the protoplasm lasts almost as 

 long as the tentacles remain inflected, even though this be 

 for more than a week; but the protoplasm is redissolved at 

 the bending place shortly before the tentacles re-expand, 

 showing that the exciting cause of the aggregating process 

 has then quite ceased. Exposure to carbonic acid causes 

 both the latter process and the motor impulse to travel very 

 slowly down the tentacles. We know that the aggregating 

 process is delayed in passing through the cell-walls, and we 

 have good reason to believe that this holds good with the 

 motor impulse; for we can thus understand the different 

 rates of its transmission in a longitudinal and transverse 

 line across the disc. Under a high power the first sign of 

 aggregation is the appearance of a cloud, and soon after- 

 wards of extremely fine granules, in the homogeneous purple 

 fluid within the cells; and this apparently is due to the 

 union of molecules of protoplasm. Now it does not seem an 

 improbable view that the same tendency namely for the 

 molecules to approach each other should be communicated 

 to the inner surface of the cell-walls which are in contact 

 with the protoplasm; and if so, their molecules would ap- 

 proach each other, and the cell-wall would contract. 



To this view it may with truth be objected that when 

 leaves are immersed in various strong solutions, or are sub- 



" [Bee Gnnllnor's Intorostlnj? mnde innrkR on the lower Burface 



rmpor " On the ('ontrnctlllty of and fonnd that when tlie curva- 



he ProtopInBin of Plant Cells " Hire take.s place, the distance be- 



(' I'roo. R. Soc.' Nov. 24, 1887, tween the iKarks on what J)e- 



vol. xllll.). In which he frlves evi- comes the convex surface of the 



dence tendhiK to show that the leaf or tentacle Increases. When 



cnrvature of the tentacles of the leaf opens, or the tentacle 



DroMorn Is brought about by con- BtralRhtens. the distance between 



traction of the protoplnflin. the marks does not return to 



liatalln (' Flora.' 1877) experl- what It was at first, and this 



mented on the curvature of the pornianent Increase shows that 



tentacles as well as on the bend- the oirvntnre Is connected with 



log of the blade of the leaf. Ue actual growth. F. D.] 



