98 



Randolph : Influence of moisture upon ivy 



In roots arising from holdfasts (class 5) the secreting cells are 

 from two to three times the size of the largest cells of that region, 

 and their ducts> like those of the holdfasts contain a yellow sub- 

 stance. 



In the roots arising from the stem in air saturated with moisture 

 (class 4) the epidermis is without root-hairs, the secreting cells of 

 the ducts are about four times the size of the largest of the neigh- 

 boring cells, and the ducts contain a brownish-black substance. 



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Figure 4. Cross-section of holdfast-root of ivy. d, the cavity of the duct (also 

 marked X) » xxv some cases there are six sets of vessels; <?/, epidermis ; v, vessels. 



Figure 5. From the stem of ivy, showing duct in the cortical parenchyma. It lies 

 near the fibro-vascular bundles. c/>, cortical parenchyma ; d 9 duct. 



In the corn-like roots which arise from the stem (class 7) the 

 secreting cells are much larger than any of the surrounding cells, 

 and the ducts (like those of the roots arising from the stem in air 

 saturated with moisture) have brownish-black contents. Granules 

 of this substance collected on the inner sides of the cell-walls 

 bordering on the lumen were especially well seen in longitudinal 

 section. These roots contain from six to nine vessels in a bundle, 

 while in all the other kinds of roots the number varies from two 

 to five. 



The ivy, Hedera Helix L., is the typical example of dimorphism 

 of shoot and leaf. * The possession of absorptive roots growing 

 out into moist air from the holdfast-roots brings the ivy into rela- 



PER 



H. Beitrtg 



Botanische I 



1892. 



