the Mycorrhiza of the Marattiaceae. 91 
on the germination of the resting spores and the subsequent infection of the 
host-plant could be attempted. 
3. Biological Relations between Host and Endophyte. 
A. Historical. 
Leaving out of consideration the research upon various ectotrophic 
mycorrhizas, an abundant literature dealing with the many views put 
forward to explain the biological significance of the association of endotro- 
phic fungi with the root, or other absorbing organ, of a number of Phanero- 
gams and Vascular Cryptogams, has accumulated during recent years. 
But full summaries and discussions of the more important results 
obtained in this field of investigation, including those of Frank (21), Noel 
Bernard (2, 7, 8, 9, 10), and Burgeff (11), are to be found in the recent 
works of Kusano (30) and of Rayner (38). Detailed reference to the 
literature is therefore unnecessary. 
The theories put forward to explain the biological significance of 
endotrophic mycorrhizas is very briefly summarized below : 
1. The mycorrhiza is a real symbiosis with reciprocal advantages; in 
other words, there is a mutual interchange of material (or other advan- 
tages) between host and endophyte (Groom (23), Macdougal (31), 
Shibata (40), &c., &c.). 
A. The higher plant provides the fungal symbiont with one or 
more of the following : 
i. Habitation. 
ii. Carbohydrate (especially starch). 1 
iii. Shelter from excess of oxygen. 2 
B. The fungus benefits the higher plant in one or more of the 
following ways : 
i. The fungus takes up humus products from the soil by 
means of its external mycelium. These humus pro- 
ducts are conducted to the internal hyphae, where they 
are converted into proteids which are in part utilized 
by the fungus in its own metabolism and in part yielded 
to the tissues of the host-plant. 3 
ii. The fungus is capable of fixing nitrogen directly from 
the air, with which it builds up organic nitrogenous 
substances (i. e. proteids) which it yields to the host- 
plant in exchange for carbohydrate material. 4 
iii. The fungus absorbs mineral salts from the surrounding 
soil. 5 
1 Corallorrhiza arizonica , Macdougal (1. c.) ; Thismia Aseroe, Groom (1. c.). 
2 Janse (1. c.). 3 Macdougal (1. c.), and others. 
4 Janse (1. c.) ; Podocarpus, Nobbe and Hiltner (34), Ternetz (42). 5 Stahl (41). 
