Structure, etc., of Epiphegus Virginiana. 375 



tracheae and some reticulated tracheids. On both sides of 

 these cells are present some small dense phloem cells. The 

 parenchyma cells lying around the bundle for some distance 

 show very greatly thickened, shining cell walls. The bundle 

 is not sufficiently well developed to afford much support. 

 So it must be these thickened parenchyma cells that give the 

 stiffness and rigidity to the grapplers. 



There has been noted a great deal of variation in the 

 production of these roots. Plants growing in a soft rich 

 soil develop a great number of them. Those already sup- 

 ported by a sandy or stony soil develop very few. This 

 seems to indicate that their chief function is one of support 

 for the parasite. But the structure of the epidermis, and the 

 richly protoplasmic, starch-filled parenchyma, render it prob- 

 able that they also possess absorbent properties. And ab- 

 sorption would also be greater in the rich humus than in 

 sand. 



The bundle can be seen passing off from a large bundle in 

 the tuber. It is quite broad here, but narrows steadily as it 

 passes out. It extends clear to the extremity of the root. 

 No trace of a root-cap has been found in any plant I studied, 

 though it has been very carefully looked for. Yet this grap- 

 pler must be considered a true root, as will be shown later. 

 The root-cap accordingly has been lost by degeneration, as 

 various investigators have already shown for other degraded 

 parasites. 



The Development of the Root. 



In very young tubers no roots have appeared on the sur- 

 face, but their internal formation is then evident. They are 

 first seen as a group of embryonic cells pushing out from 

 one of the undifferentiated central bundles of the tuber. 

 This group of cells advances through the tissues of the 

 tuber, leaving behind it a gradually forming bundle, that 

 becomes the central bundle of the root. By the time this 

 advancing group of cells has reached the circumference of the 



