462 Gregory : Effects of pressure on roots of Vicia Faba 



In the third group of experiments, which includes the roots 

 subjected to an extreme amount of pressure varying from 1400 to 

 2000 grams, marked changes had taken place. The plerome 

 cells were well broken up. Splits had appeared in the periblem 

 layer, and groups of both plerome and periblem cells were greatly 



displaced (see figure 2). 



In general, the greatest amount of injury was found in the 

 region directly posterior to the initial meristematic region. Roots 

 which had been subjected to the greatest amount of pres- 

 sure showed cavities and rifts in all regions and in many cases 



Figure 4. Displaced plerome cells from region F in figure 2, showing elong- 

 ated cells which have become further differentiated into fibrovascular tissue. X 53*^* 



displacement of single cells or masses of cells. The protoplasm 

 of the cells on the edges of the rifts was very much vacuolated 

 and the nuclei were distorted in many cases ; a few, however, had 

 assumed a normal condition (see figure 3). Plerome cells, 

 which had been forced into the extreme anterior portion of the 

 root, showed evidences of further differentiation into the future 

 vascular system (see figure 4). Thus we may conclude that ^. 

 not even a maximum amount of pressure, nor an absolute change 

 h) environment will entirely stop or affect the normal development 

 of the cells of Vicia Faba. 



Botanical Laboratory, Barnard College, 

 Columbia University. 



