SAPROPHYTISM AND SYMBIOSIS 



799 



development in association with root fungi. Between extreme auto- 

 phytes such as the crucifers and obligate mycophytes such as the orchids 

 there exist all gradations; for example, liverworts such as Preissia and 

 Fegatella are facultative mycophytes, growing either with or without 

 fungi. Generally in autophytes roots and root hairs are well developed, 

 starch is abundant, transpiration is relatively intense, and growth is 

 rapid, while in obligate mycophytes root development is weak, root hairs 

 are few or wanting, transpiration is slight, and growth is slow. 



Even though the total number of mycophytes may surpass that of 

 the autophytes, it is not to be inferred that fungal hyphae surpass root 

 hairs in importance in green plants as a whole, for the majority of my- 

 cophytes have root hairs and only a relatively sparse development of 

 root fungi; probably many of these plants are facultative mycophytes 

 in which the fungal relation is relatively casual and is attended with no 

 particular benefit or injury to either symbiont. But the importance of 

 fungi in the nutrition of the higher plants probably is much greater than 

 generally has been suspected, in spite of the fact that the matter may be 

 one of great economic importance. It is very likely that the well-known 

 difficulty in cultivating many of the Pinaceae, Fagaceae, Orchidaceae, 

 and Ericaceae, as contrasted with the ready cultivation of the Cruci- 

 ferae and Rosaceae, may be due to the fungal symbiosis of the former; 

 many orchids are now grown successfully by taking care that conditions 

 are made suitable for their fungi. Very probably the ability of many 

 plants (such as the ericads) to flourish in bogs, where nitrogen fixation 

 or nitrification by bacteria is relatively rare, is because they live symbi- 

 otically with fungi which are capable of fixing nitrogen. It is common 

 to picture organic life chains leading from such dependent forms as ani- 

 mals or fungi back to green plants, which in the sunlight manufacture 

 foods from inorganic raw materials. A truer picture of the plant king- 

 dom is one that recognizes symbiosis, bringing out the dependence of 

 mycophytes upon their fungi, of legumes upon their bacteria, and of 

 other green plants upon the soil bacteria, as well as the dependence 

 of all of these lower forms upon the green plants. 



The origin of myco symbiosis. There is no adequate evidence upon which to 

 base speculations concerning the origin of mycorhizal phenomena Very probably 

 the initial phases resembled those postulated for the origin of parasitism, and chem- 

 otropic reactions may well have played an important part ; indeed, it has been 



holosaprophytism in the higher plants (such as in Lycopodium, Monotropa, and Corallo- 

 rhiza) are to be referred to symbiotic saprophytism or mycophytism. 



