220 TRILLIUM. 



have a common origin, but are distinct from the first. 

 Lateral members soon appear as small protuberances, 

 which are rudimentary leaves, branches, or roots, those 

 nearest the apex being the youngest. The axis 

 remains so short that the lower leaves overlap the 

 growing point, and in the case of this underground stem 

 thicken and coalesce at their tips, forming a continuous 

 and firm sheath, thus performing the same office of pro- 

 tection for the rootstock that the root-cap does for 

 roots. In the same Trillium bud may be seen the 

 essentially different mode of development of the root 

 and branch, the former being endogenous and pushing 

 its way through the overlying tissues, the latter exog- 

 enous, 18 blending with the surface tissues of the stem. 



The branch, or aerial stem, is remarkable for its sin- 

 gle long internode. The fibro-vascular bundles are 

 rather poorly developed, the monocotyledonous stem 

 bundle being more typically represented in Avena. In 

 Trillium, however, are seen such monocotyledonous 

 characters as the isolation of the bundles within an 

 abundant fundamental parenchyma, the well-marked 

 phloem and xylem areas with no intervening cambium 

 (closed bundles), and an occasional development of an 

 external sheath. 14 



The histology of the leaf is in general much the 

 same as in the majority of leaves ; it differs from Avena 

 in the presence of a much better developed mesophyll. 

 A broader expanse of leaf tissue necessitates a greater 

 branching of the supporting and conducting fibro-vas- 

 cular system, and a better differentiation of leaf sur- 



18 Prantl and Vines, op. cit., p. 23. 

 14 Prantl and Vines, op. cit., p. 58. 



