678 



THE AMERICAN NATURALIST 



[Vol. XLVI 



A root 2.0 mm. in diameter shows the usual divisions 

 into central cylinder and cortex. The endodermis is 

 well marked. The epidermis is discolored and bears the 

 remains of root-hairs. Cork has not begun to form, how- 

 ever. The cortex is composed of cubical parenchyma; 

 the parenchyma of the central cylinder offers no un- 

 usual features. Little starch or crystals are to be seen. 



Structure of the Parasitic Eoots 

 The roots of Cissus, which developed within the tissues 

 of the cactus, varied in diameter from 2 to 5 mm. and 

 showed characteristics which were in certain regards 

 quite different from those of the free-living roots ex- 

 amined. 



If a cross-section of a root 2 mm. in diameter is studied 

 the usual differentiation into cortex and central cylinder 

 will be noted. The cortex is composed of relatively large 

 cells a few of which contain stellate crystal aggregates 

 and raphides. A layer of cork, over half dozen cells in 

 thickness, bounded by the dead remains of the epidermis. 



