Randolph : Influence of moisture upon ivy 



97 



In the common roots that grow out in water from the stem 

 (class 3) the parenchyma has very thin walls, and thus the epi- 

 dermis and the endodermis are sharply differentiated from it. In 

 these roots, and in the roots that grow out from them after trans- 

 plantation into earth, the secreting cells are about the size of the 

 cells of the surrounding tissue. The secreting cells contain dense 

 protoplasm and the ducts are empty. The sclerenchyma of the 

 central column is shaped in transverse section like a sharp-pointed 

 star (figure 3). 



In the following kinds of roots the ducts have contents 



and 



the central sclerenchyma cells are more numerous and in section 

 resemble a regular pentagon. Hence the phloem is farther re- 

 moved from the center of the stem and the endodermal ring is 

 larger than in common water roots, etc. 



Figure 3. Cross-section of absorptive root springing from the submerged part of the 

 stem of ivy in water, d, duct ; en\ endodermis ; ep, epidermis; h, hair; v 9 vessels. 



In the holdfasts (class 2) the epidermis is from two- to three- 

 layered, and root-hairs are entirely absent or sparse (figure 4). 



Adjoining or very near to each set of vessels of the holdfast- 

 roots and on their peripheral side is a duct containing a yellowish 

 substance and bounded in cross-section by four cells. This sub- 

 stance is probably the cement by which the holdfast-roots adhere 



to foreign 



f Ducts are present in the cortical paren- 



chyma of the stem, with contents apparently similar but with walls 

 consisting of a greater number of cells (figure 5). 



* The roots here described were all preserved in Flemming's solution, 

 f Darwin, C. Climbing plants 187, 188. 



