THE METHOD OF MOVEMENT 141 



aeration and Parkin (1899) has found that sugar absorption, 

 as tested by starch deposition in leaf tissues floated on 

 sugar solution, is dependent upon adequate aeration. 



I am of the opinion that outer plasmatic membranes are 

 relatively impermeable to sugars and that the plasmodesma 

 offer ready channels through which diffusion from cell to 

 cell may take place without passage through surface 

 membranes. Kienitz-Gerloff considered that moving pro- 

 toplasm is concerned in actually carrying organic material 

 from cell to cell in all parts of the plant and that such flow 

 is not restricted to sieve tubes where connections from 

 segment to segment are relatively coarse. He claimed 

 to have demonstrated that, with the exception of guard 

 cells, all parts of a given individual are interconnected 

 by plasmatic strands thus forming a single unified organism. 

 He stated that movement seems not impossible, for the 

 strands in many cases are no finer than the visibly moving 

 strands in the hairs of Cucurbita. He suggested that 

 protoplasmic contents may actually be withdrawn through 

 these connections from maturing vessels, sclerenchyma 

 fibers, and cork cells and that the autumnal emptying of 

 leaves takes place largely through these connections. The 

 failure of guard cells to empty when placed in the dark or 

 during autumnal emptying, he explained as due to the 

 complete absence of these connections. In a later paper 

 (1902) he reported the finding of plasmodesma in guard 

 cells thus confirming the observations of several others 

 who had reported them subsequent to his earlier paper. It 

 seems significant that the plasmodesma when found in 

 guard cells are restricted to pits and are not scattered over 

 the surface as in ordinary epidermal or parenchyma cells. 

 His contention that protoplasm actually moves through 

 the plasmodesma seems not to have been accepted but 

 on the contrary has been specifically denied. I am of the 

 opinion, however, that it is definitely worth reinvestigating. 

 Miehe (1901) has reported the movement of nuclei and 

 protoplasm through plasmodesma in response to wound 

 stimuh. Miinch (1930) (see Sec. 28) assumes that there 



