SYMBIOSIS OF PHANEROGAMS AND FUNGI. 249 



SYMBIOSIS OF GREEN-LEAVED PHANEROGAMS WITH FUNGAL MYCELTA 

 DESTITUTE OF CHLOROPHYLL.— MONOTROPA. 



Another instance of symbiosis is observed to exist between certain flowering 

 plants and mycelia of fungi. The division of labour consists in the fungus-mycelium 

 providing the green-leaved Phanerogam with water and food-stuffs from the ground, 

 whilst receiving in return from its partner such organic compounds as have been 

 produced in the green leaves. 



The union of the two partners always takes place underground, the absorbent 

 roots of the Phanerogams being woven over by the filaments of a mycelium. The 

 first root that emerges from the germinating seed of the phanerogaKiic plant 

 destined to take part in the association descends into the mould still free from 

 hyphaj; but the lateral roots and, to a still greater extent, the further ramifications, 

 become entangled by the mycelial filaments already existing in the mould or 

 proceeding from spore-germs buried there. Thenceforward the connection 

 continues until death. As the root grows onward, the mycelium grows with it, 

 accompanying it like a shadow whatever its course, whether the root descends 

 vertically or obliquely, or runs horizontally, or re-ascends, as is sometimes necessary 

 when it happens to be turned aside by a stone. The ultimate ramifications of roots 

 of trees a hundred years old, and the suction-roots of year-old seedlings, are woven 

 over by mycelial filaments in precisely the same manner. These mycelial 

 filaments are always in sinuous curves and intertwined in various ways, so that 

 they form a felt-like tissue, which looks, in transverse section, delusively like a 

 parenchyma. As regards colour the cell-filaments are mostly brown, sometimes 

 they are almost black, and it is rare for them to be colourless. The epidermis of 

 many roots is covered as if by a spider's web, whilst the hyphse form a complex 

 tangle of bundles and strands bz'oken here and there by open meshes through which 

 the root is visible. In other cases an evenly woven but very thin layer is wrapped 

 round the root; and in others, again, the fungus-mantle forms a thick layer which 

 envelops uniformly the entire root (see fig. 59). Here and there the hyphse 

 insinuate themselves also inside the walls of the epidermal cells, and the latter are 

 pei-meated by an extremely fine small-meshed mjj^celial net (see fig. 59^). 

 Externally the mantle is either fairly smooth and clearly marked off" from the 

 environment, or else single hyphse and liundles of hyphse proceed from it and 

 thread their way through the earth. When these branching hyph» are pretty 

 equal in length they look very much like ordinary root-hairs. And they not only 

 resemble them, but assume the function of root-hairs. The epidermal cells of the 

 root, which would in an ordinary way act as absorption-cells, being inclosed in the 

 mycelial mantle cannot exercise this function, and have relegated the business of 

 sucking in liquid from the ground to the mycelium. The latter undoubtedly acts 

 as an absorptive apparatus for the partner on whose roots it has established itself; 

 and the water in the soil, together with all the mineral salts and other compounds 



