8 Weiss, XenopJiyton I'adicitlosuvi (Hick). 



rootlets will be seen to be given off in a manner equally 

 typical of Stigmaria {Plate XI., Fig. 2), leaving broad 

 medullary rays opposite the outgrowing bundle, which 

 represents a complete segment of the vascular elements 

 of the stele with the protoxylem on the inner face. As 

 is seen from the longitudinal section, the bundle is given 

 off very obliquely at first. As there is very little secondary 

 growth in the stele, we do not find that horizontal 

 connecting piece running in the medullary ray, which must 

 necessarily be formed as the secondary tissues increase in 

 thickness. 



The vascular branch carries with it a portion of the 

 phloem on the outside, just as do the leaf-trace bundles in 

 the stems of the Lepidodendre(B^ and each may be con- 

 sidered as monarch if we adopt the usual terminology of 

 roots. In passing outwards, the vascular supply to the 

 roots will be seen to be enveloped by a sheath of cells, 

 in direct continuity with the inner cortex {Plate^A., Fig. 2, 

 and P late YAl., Fig. i). 



A great amount of meristematic activity seems to take 

 place in tissues of the middle cortex, especially on the 

 inside of the bundle running to the rootlet. Here, by 

 division of the cortical cells, a little cushion of smaller 

 cells is formed, often showing clearly their secondary 

 origin, as in Hick's Fig. 6. Sometimes the tissues are, 

 however, less regularly arranged, as in Plate XII., Fig. 2, of 

 the present paper, where the secondary cells on the inside 

 of the rootlet are clearly distinguishable from the primary 

 cortex of the Stigmaria by their smaller size and by the 

 distinct line of demarcation due to a compression of the 

 adjoining cells. 



As the rootlet-bundle passes further outwards, it 

 comes to lie more centrally, and ultimately completely, in 

 the middle of this proliferation ot the middle cortex, 



