NUTRITION. l6l 



C. Nutrition of colorless plants. 



216. Colorless plants. — By this really inaccurate phrase 

 are meant plants which do not possess chlorophyll, though 

 some of them are highly colored by other pigments. 



The colorless plants among the thallophytes constitute two 

 large groups, known as bacteria and fungi. Among the seed 

 plants, also, are found some devoid of chlorophyll. 



Many plants possessing chlorophyll show to the eye other 

 tints than green, when other pigments are present in such 

 quantity as to mask the green. This is notably the case with 

 the so-called "foliage plants," in which reds, yellows, pur- 

 ples, and browns are common. (See also ^[ n, 40, 4 3?) 



Colorless plants necessarily live either upon the decomposi- 

 tion products of dead organisms, or in company with living 

 organisms. Those which live upon dead bodies, whether 

 these have lost their form completely or not, are known as 

 saprophytes. Those organisms which live in association one 

 with another are called symbionts and their relation is known 

 as symbiosis. (See Chap. XXIV.) Some symbionts are 

 antagonistic and stand in the relation of parasite and host, 

 the name parasite being applied to the organism which 

 depends for its food upon the supporting organism, called the 

 host. 



217. Saprophytes and parasites may be either obligate or 

 facultative. Obligate parasites or saprophytes are those which 

 can exist only upon living or upon dead organisms, respec- 

 tively. Facultative parasites or saprophytes are those which 

 can pass a portion of their existence upon decaying or upon 

 living organisms, respectively. They are not able, however, 

 to complete their life cycle except upon their appropriate 

 substratum. 



218. Saprophytes. — Saprophytic bacteria live immersed 

 in solutions of organic material, or surrounded by films of 



