252 



STUDIES IN. FOSSIL BOTANY 



keep the internal cortex in place, we seldom find it in 

 its natural central position ; usually it is more or less 

 excentric. It consists of a few layers of delicate 

 parenchyma ; an endodermis has not yet been dis- 

 tinguished. 



We now come to the vascular strand, which occupied 



Fig. 102. —SHgmaria. ficoides. Part of transverse section of rootlet, to show monarch 

 structure, px, protoxylem, at one corner of the thick-walled strand of wood ; //*, 

 phloem, which thins out opposite the protoxylem ; z'.c, inner cortex ; o.c, part of outer 

 cortex. X about 50. From a photograph by Dr. Bousfield. S. Coll. 114. 



the central position in the whole structure. As a rule 

 the wood only remains ; occasionally, as in the specimen 

 shown in Fig. 102, the delicate tissue which no doubt 

 constituted the phloem, and perhaps the pericycle 

 also, is preserved. We will consider the xylem first. 

 It consists of a small strand of tracheides with a some- 

 what triangular transverse section (Figs. 101-105). One 



