STIGMARIA 253 



angle is more prominent than the others, and is in 

 contact with the surrounding parenchyma (Figs. 102- 

 104, px). At this angle the smallest elements are 

 situated, and longitudinal sections show that they alone 

 are spirally thickened ; the remaining elements of the 

 xylem are scalariform. It is therefore clear that the 

 rootlet had only a single group of protoxylem, and 

 thus, if we are to adopt the terminology usual in the 

 case of roots, must be termed monarch. This conclu- 

 sion is confirmed by the comparison of rootlets at 

 .various stages of growth, which always show the first 

 differentiated tracheae at one angle only, never at three. 

 So far as the English specimens are concerned, there 

 can be no doubt that in S.ficoides all the appendages 

 agree in having a monarch vascular strand. 



A remarkable feature in the structure of the Stig- 

 marian rootlet has recently been investigated by Professor 

 F. E. Weiss. 1 Renault in 1882 had described rootlets 

 with a very delicate vascular strand given off from the 

 stele, and had regarded this as indicating a mode of 

 branching distinct from the usual dichotomy. Professor 

 Weiss confirms this observation (on which some doubt 

 had been cast), but finds that the vascular strands in 

 question have no connection with branches. They 

 consist of spiral tracheides, and start from the proto- 

 xylem, pass out, obliquely or horizontally, through the 

 middle cortex, enclosed in a sheath or traversing a 

 trabecula, and terminate in connection with an extensive 

 patch of tracheidal tissue in the outer cortex (Fig. 103). 



1 "On Xenophyton radiculosum and on a Stigmarian Rootlet," Mem. 

 and Proc. Manchester Lit. and Phil. Soc. vol. xlvi. 1902 ; "The Vascular 

 Branches of Stigmarian Rootlets," Ann. of Bot. vol. xvi. 1902; "The 

 Vascular Supply of Stigmarian Rootlets," ibid. vol. xviii. 1904. 



