362 



STRUCTURE OF PHANEROGAMIC PLANTS. 



towards its circumference. It is obvious that fluids will be more 

 readily transmitted in the direction of greatest elongation, being 

 that in which they will have to pass through the least number of 

 partitions ; and whilst their ordinary course is in the direction of 



FIG. 150. 



Sections of Cellular Parenchyma of Aralia. or Rice-paper Plant; A, transversely to the axis of the 

 stem; B, in the direction of the axis. 



the length of the roots, stem, or branches, they will be enabled, 

 by means of the medullary rays, to find their way in the trans- 

 verse direction. One of the most curious varieties of form which 

 Vegetable cells present is that represented in Fig. 151, which 

 constitutes the stellate cell. This 

 modification, to which we have Fl - 152 - 



already seen an approximation in 

 the Volvox ( 159), is found in the 

 spongy parenchymatous sub- 

 stance where lightness is an ob- 

 ject; as in the stems of many 



FIG. 151. 



Section of Cellular parenchyma of Rush. 



Cubical parenchyma, with stellate cells, from 

 petiole of Nuphar lutea. 



aquatic plants, such as the Rush, which need to be furnished 

 with air-spaces. In other instances, these air-spaces are large 

 cavities, which are altogether left void of tissue ; such is the case 



