758 ECOLOGY 



food when the conditions are favorable for autophytism. It has been 

 claimed, but scarcely proven, that root hairs secrete enzyms, as do fungi. 

 Results similar to those obtained in maize have been reported in the vetch, 

 the cress, and the radish, and it is very probable that many if not most 

 green plants have a greater or less capacity for partial saprophytism. 



Some seed plants (principally among the Scrophulariaceae) that commonly are 

 partial parasites (p. 772) are said to be saprophytic in some cases; for example, 

 Melampyrum develops haustoria among dead leaves and becomes attached indiffer- 

 ently to dead or to living roots. Even those species which become attached only to 

 living hosts continue to derive nourishment therefrom after the latter are dead. 

 Lathraea, which commonly is a holoparasite (p. 772), sometimes lives as a sapro- 

 phyte. It has been claimed that certain mosses with few leaves (as Buxbaumia) are 

 partially saprophytic; apart from the sparse foliage, the only argument for this 

 view is the fact that the rhizoids penetrate among dead leaves and sometimes have 

 knoblike processes resembling haustoria. 



While much is yet to be learned about saprophytism in the seed plants, 

 it certainly is an odd circumstance that the plants least likely to exhibit 

 saprophytism are forms like Monotropa, which once were regarded 

 as holosaprophytes, while saprophytism is best evidenced in such plants 

 as maize, which has been regarded as a representative autophyte. 

 However, the nutritive evolution of heterotrophic seed plants as a class 

 seems rather to have been in the direction of symbiotic saprophytism 

 (p. 798). 



The origin of saprophytism. The prevalent conception of the origin 

 .of saprophytism is that from time to time saprophytic branches have 

 diverged at various levels from the main autophytic trunks. The sapro- 

 phytic fungi and bacteria do not appear to form an independent and 

 connected genetic line, but occur as disconnected groups, some of which 

 resemble algae of widely different families. For example, in form and 

 structure and in method of reproduction the bacteria resemble the blue- 

 green algae, differing from them chiefly in the general absence of food- 

 making pigments and in their much smaller size; the close relationship 

 between these groups is emphasized further by the great saprophytic 

 capacity of the blue-green algae, by the pigmentation of certain bacteria 

 and fungi, 1 and by the fact that various bacteria are able to manufacture 

 carbohydrates. Both among the bacteria and the blue-green algae there 



1 Notable among the pigmented forms are the purple bacteria, which contain, in addi- 

 tion to the purple pigment, a green pigment that resembles chlorophyll. Manilla silophila, 

 a fungal form, is colorless when grown in the dark, but when grown in the light, it ex- 

 hibits an orange color due to carotin. 



