378 



BOTANY 



en 



The Root 



The primary or tap-root of the Monocotyledons never persists, and 

 the roots never show a secondary thickening, although in the Palms 



and Pandanaceae they 

 may be several centi- 

 metres in diameter. 

 Aerial roots are com- 

 mon, especially among 

 tropical forms, like the 

 epiphytic Orchids and 

 Araceae, and some 

 Palms and Pandana- 

 ceae. In the latter they 

 may originate upon the 

 trunk far above the 

 surface of the ground, 

 or even from the 

 branches. 



xn- 



FIG. 349. Phcenix Canariensis, cross-section of the 

 vascular cylinder of the primary seedling root 

 (X<00); m, medulla; x, xylem; ph, phloem; p, 

 pericycle ; en, endodermis. 



The typical root (Fig. 

 348) shows three layers 

 of meristem at the apex, 



plerome, periblem, and calyptrogen, but there may also be a distinct derma- 



togen. The root-cap is ^ 



well developed, and in ^ ^ C A 



aerial roots it often forms 



an extremely conspicuous 



spongy body, which is of 



importance in absorbing 



moisture. Roots are quite 



absent in Corallorhiza, 



where they are replaced 



by branching rhizomes, 



and this is probably 



true of other saprophytic 



forms. In these there is a 



mycorhiza or endophytic 



Fungus present, which is 



of importance in the nutri- 

 tion of these forms. 



The Flower 



FIG. 350. ^, Calochortus luteus, var. oculatus. B-E, 



In the simplest C.venu&tus. , stamen (X2). C, cross-section of 

 flowers like those of anther (X 4). D, capsule (natural size). E, cross- 

 -VT section of young capsule ( X 2) . 



Naias, or some Araceae 



(Fig. 352), the flower may be reduced to a single carpel or stamen. 

 In many of these forms the ovule is terminal, i.e. is derived from 



