218 TRILLIUM. 



Hum may be mentioned as by far the most common 

 form.. 



As in Adiantum, the main axis of Trillium is subter- 

 ranean, horizontal and thickened, forming a rootstock, 

 a protective measure which in this case is correlated 

 with spring blooming and a long period of rest. The 

 aerial part of Adiantum, however, is a leaf, while in 

 Trillium it is a branch, the " root-leaves " being 

 reduced to membranous scales on the rootstock. A 

 single branch (rarely two) is sent above ground each 

 season, and a series of corresponding annual scars may 

 frequently be seen upon the stem. In the meantime 

 the terminal bud of the latter continues to develop 

 and to thrust its way through the soil, protected in 

 this root-like habit by a special modification of bud- 

 scales. 



Probably the most exceptional character of Trillium 

 is the venation of its foliage leaves, which is of the 

 netted type, instead of the parallel venation most 

 characteristic of monocotyledons, as in Avena. Among 

 net-veined leaves they are palmate, a type which pro- 

 duces a broad expanse of surface, very favorable for the 

 accomplishment of leaf work. In this way Trillium has 

 secured a large exposure of surface to air and sunlight 

 for a plant so low in stature, and generally deeply sunk 

 in vegetable debris. 



The primary root-structure is quite uniform in all 

 plants, consisting of epidermis (or a piliferous layer), 

 cortical parenchyma, and a central nbro-vascular cylin- 

 der. In the central cylinder xylem and phloem masses 

 alternate with each other, the intervening spaces being 

 occupied by parenchyma (forming a radial bundle) ; sur- 



