RACHIOPTEEIS CYLINDRICA. • 57 



The Cortex. 



The cortex is, apparently, cellular throughout, but the outer part is 

 usually more or less differentiated from the inner. The former, or 

 hypoderma, consists of elements which in the transverse section are 

 polygonal, or rounded in shape, and of relatively large size. The walls 

 show some degree of thickening, which, however, diminishes from 

 without inwards. Longitudinal sections show the elements to be 

 much elongated in that direction, and, in form and appearance, to be 

 sclerenchymatous. 



The inner part of the cortex is composed of cells which are some- 

 what smaller and rounder in transverse section than the elements of 

 the hypoderma. Towards the stele they diminish in size, become 

 somewhat compressed radially (as was noted by Williamson), 1 and are 

 arranged in concentric layers. They show a certain amount of wall 

 thickening, which increases from without inwards, and the innermost 

 elements are elongated longitudinally. In the middle part of the 

 cortex, where the hypoderma and the inner parenchyma run into one 

 another, the cell walls are thinner and often much crumpled. In 

 young specimens a complete zone of thin- walled elements occupies this 

 region, but in older ones it is occupied by a series of radial lacunae, 

 separated by cellular partitions (Fig. 1). From the appearance of the 

 tissues abutting on these lacunas, it seems probable that their origin 

 was lysigenous rather than schizogenous. 



The contents of the cortical elements are somewhat remarkable, and 

 present some interesting modifications. In one or two specimens the 

 contents of both hypoderma and inner parenchyma are in the form of 

 contracted utricules, as may be seen in the marginal section on No. 

 102. But in the second section on the same preparation, as well as in 

 other cases, the utricular form is restricted to the hypoderma, and the 

 contents of the inner parenchyma are in the form of granules, which 

 remind us of the stored starch of recent plants. In the majority of 

 the preparations, however, the cortical cells contain certain sharply 

 defined black bodies, of a rounded or ellipsoidal shape, and with an 

 even contour (Fig. 2). Frequently they are seen to be enclosed in a 

 sort of vesicle, the cavity of which they do not fill, and whose wall is, 

 therefore, somewhat removed from the body itself. The bodies are 



1 Loc. cit. p. 350. 



