TRILLIUM RECUR VA TUM. 219 



rounding all is a layer of parenchyma, the pericambium, 

 and outside of this a single layer of modified cortical 

 cells, the bundle sheath or endodermis. Rootlets of 

 most cryptogams originate from the bundle sheath, 

 while in phanerogams they usually come from the peri- 

 cambium. 10 In the radiating lines of tracheary vessels 

 it will be noticed that the larger vessels are toward the 

 center, the smaller spiral vessels being peripherally 

 placed, thus reversing the order of the stem. 11 



The stem is very much modified by becoming a food 

 reservoir. The epidermis is poorly limited, often 

 scarcely distinguishable from the adjacent cortical 

 parenchyma ; the parenchyma of the fundamental 

 system is greatly developed and filled with starch ; 

 while the fibro-vascular bundles are reduced and 

 irregular in their course. In most cases the bundles 

 bend outwards, and such are evidently leaf-traces, 1 * 

 though they have lost all definite connection with the 

 accompanying scale-like leaves. 



The terminal bud of the stem is large and its parts 

 very distinct. It is taken to represent in our series a 

 typical terminal bud of phanerogams. A section 

 reveals the fact that the growing point (piinctum vege- 

 tationis) consists of a group of cells, in place of the 

 single apical cell of cryptogams, and the forming tis- 

 sues diverge from it in well defined lines. The three 

 typical regions of the stem originate from different 

 regions of this primary meristem, so that they do not 



10 Prantland Vines, Text-book, p. 51; Strasburger, Bot. Pract., p. 276. 



11 Cf. Goodale, Physiol. Bot., p. no, et seq. ; Prantl and Vines, Text- 

 book, p.5i;DeBary, Comp. Anat., p. 348. 



12 Cf. Prantl and Vines, Text-book, p. 46; Goodale, Physiol. Bot., p. 

 125; DeBary, Conip. Anat., p. 233. 



