PAEA8ITIC AND SAPROPHYTIC PLANTS. 



43 



or rarely so, in ordinary flowering plants. Perhaps the nearest approach 

 to them may be seen in members of the order Lecjuyninosce. These 

 produce nodules on their roots, and very large coral-like masses occur on 

 the roots of Cytisus Laburnum, very suggestive of the rhizomes of the 

 saprophyte Corallorrhiza, a^i orchid. A closer analogy obtains between 

 them in that they are infested by fungi. The fungus, assuming a 

 bacterioid form in the Leguminosce, is supposed to be able to fix the 

 nitrogen of the air, which, by some mysterious power, is conveyed to the 

 host plant, w^hich is thereby benefited by the process. This union of two 

 organisms where one benefits, without preying upon the other, is called 

 " symbiosis." In the case of saprophytes a mycelioid fungus invests the 

 surface or deeper layers of the cells of the root. This is called Mycorrhiza, 

 and the richer the soil the more marked is its presence. In Sarcodes 

 (ord. Monotropacece), a saprophyte of California, Professor Oliver found 

 that it forms a dense felt-like covering over the roots, the fibres penetrat- 

 ing between and separating the epidermal cells, but they do not penetrate 

 deeper in that plant. In Neottia and Corallorrhiza they invest and enter 

 the large cells of the cortex, which contains much nitrogenous matter. 



These discoveries * were first made in 1840, and it was suggested by 

 Pfeffer, in 1877, that the mycelium and the host had a symbiotic connec- 

 tion. It was Frank, in 1885, who emphasised its importance and carried 

 out experiments to prove its reality. In conifers and amentales the 

 fungus is external or " ectotrophic " ; but in orchids and a vast number 

 of other plants it is internal or " endotrophic." 



In the case of the former Frank regarded the mycehum as a substitute 

 for root-hairs, fulfilling their function. The fungus was thus supposed to 

 absorb nourishment, such as mineral salts and nitrogenous matters, from 

 the humus and convey them into the roots of the " host." 



In return the plant, it was thought, supplied hydrocarbons to the 

 fungus. 



Frank's experiment consisted in sowing fifteen beech seeds in humus, 

 which developed properly ; but fifteen in sterilised humus and in quartz 

 sand either died or remained stunted. 



From 1885 to 1894 saprophytic angiosperms were much studied, and 

 the constant presence of endophytic fungi in their greenless parts proved 

 to exist. The fungus occurring in the tuberous roots of orchids was 

 believed to have been traced to belong to Fusarium and Nectria. 



Sarauw, however, in 1904 showed that the mycelium was not so 

 indispensable to their arboreal " hosts " as Frank had supposed. Many 

 roots grew rapidly, and so freed themselves from the mycelial covering. 

 Moreover Von Tabeuf, in 1903, showed that radical hairs are by no means 

 totally absent and many roots had no mycelial investment. He thought 

 the ectotropic fungus absorbed salts for itself from the humus and made 

 nitrates for the angiosperms. Stahl also had, in 1900, observed that trees 

 supplied with plenty of water abounded in starch and salts and were 

 devoid of mycorrhiza ; but those with a deficiency, comparatively speaking, 

 had more sugar and were always associated with mycorrhiza, receiving 



* The following is a brief epitome of important facts in a series of papers by 

 M. Gallaud, " Etudes siir les Mycorrhizes Endotrophes," in Bev. Gin. de Bot. vol. xvii. 

 1905. 



