No. 495] SYMBIOSIS IN FERN PROTHALLIA 



155 



presumably secures lodging, but not board, from its 

 host. 



The symbiotic association of fungi with green plants 

 was first demonstrated in the lichens, hut it is now known 

 that many of the higher plants are regularly associated 

 with fungi in what is undoubtedly a symbiotic relation. 

 The best known cases of these are the mycorhizal fungi 

 connected with the roots of many trees, especially the 

 Cupuliferae, and those which occur in the tissues of sapro- 

 phytes growing in humus. These humus saprophytes 

 are especially numerous among the Orchidacce. > . t/.. 

 Neottia, Corallorhiza, Cephalanthera, etc., and in certain 

 forms of the Ericales. The well-known Indian pipe, 

 Monotropa uni flora, and the snow plant of the Sierra 

 Nevada, Sarcodes sanguinea, are well known examples 

 of these saprophytic Ericales. Many Orchidacea? and 

 Ericaceae which possess chlorophyll are also to a greater 

 or less extent saprophytic and show a well-developed 

 mycorhiza. In the case of chlorophylless plants, there 

 can be little doubt that the fungus enables them in some 

 way to utilize carbonaceous compounds from humus. In 

 the case of plants such as the trees referred to, where 

 there is ample chlorophyll tissue, it is more likely that 

 the role of the mycorhiza is rather to supply nitrogen 

 than carbon, and it is highly probable that in the case 

 of chlorophylless saprophytes as well, the fungus pro- 

 vides nitrogen. This has recently been demonstrated 

 for the mycorhiza found in the roots of various Ericaceae, 

 e. g., species of Erica, Vaccinium, Calluna and Oxycoecus 1 

 In all of these it was shown that the fungus concerned, 

 which seemed to be a species of Phoma, was able to as- 

 similate free nitrogen in much the same way as is done 

 by such nitrogen bacteria as Azotobacter. 



A very complete study of the endophytic fungi of roots 

 has been made by Janse. 2 He examined a very arge 



