382 



PKACTICAL BOTANY 



along the surface of the stems- by the 

 aid of special absorbent hairs which 

 grow from the epidermis. This plant 

 can become almost dried up without 

 permanent injury. Orchids like Cattleya 

 (Fig. 20) frequently have long, dan- 

 gling roots, covered with an absorb- 

 ent layer of tissue which acts much like 

 blotting paper, taking up water very 

 promptly, and gradually releasing it for 

 the use of the plant. Many epiphytes of 

 this type have thickened, fleshy stems, 

 or leaves, or both, and a thick epidermis, 

 through which little water escapes. 



350. Saprophytes. In general, the 

 seed plants which are saprophytes occur 

 only in the forest or under shrubs. It is 

 in such situations that plants find a most 

 abundant supply of humus, or decaying 

 organic matter. Complete saprophytes 

 that is, those which cannot exist without 

 an abundant supply of soluble organic 

 matter in the soil or substratum are 

 always pale, or even white, from partial 

 or complete absence of chlorophyll (Figs. 

 307, 308). Their leaves are small and 

 scale-like. Their roots are usually short, 

 little branched, and furnished with a 

 mycorrhiza, which freely absorbs plant 

 food from the substratum. 



Partial saprophytes, among flowering 

 plants, are not easily recognized by 

 their form and color, but may be known 

 by their inability to nourish without FIG. 308. Pinesap (Mono- 



considerable humus in the soil. Their re- tropaHypopitys), a yellow- 

 ish symbiotic saprophyte, 

 quirements in this respect diner greatly, dependent on mycorrhiza 



