The conception of an advantageous symbiosis of fungi with other plants has become familiar to us in Orchids and in the mycorhizal formation on the roots of trees, shrubs, etc. Fungal hyphae are also frequent inhabitants of the rhizoids of hepatics though, according to Gargeaune[259], the benefit to the hepatic host-plant is doubtful. An association of fungus and green plant of great interest and bearing directly on the question of mutual advantage has been described by Servettaz[260]. In his study of mosses, he was able to confirm Bonnier’s[261] account of lichen hyphae growing over such plants as _Vaucheria_ and the protonema of mosses, which is undoubtedly hurtful; but he also found an association of a moss with one of the lower fungi, _Streptothrix_ or _Oospora_, which was distinctly advantageous. In separate cultivation the fungus developed compact masses and grew well in peptone agar broth. Cultures of the moss, _Phascum cuspidatum_, were also made from the spores on a glucose medium. The specimens in association with the fungus were fully grown in two months, while the control cultures, without any admixture of the fungus, had not developed beyond the protonema stage. Servettaz draws attention to the proved fact that, in certain instances, plants benefit when provided with substances similar to their own decay products, and he considers that the fungus, in addition to its normal gaseous products, has elaborated such substances, as acid products, from the glucose medium to the great advantage of the moss plant. A symbiotic association of _Nostoc_ with another alga, described by Wettstein[262], is also of interest. The blue-green cells were lodged in the pyriform outgrowths of the siphoneous alga, _Botrydium pyriforme_ Kütz., which the author of the paper places in a new genus, _Geosiphon_. The sheltering _Nostoc symbioticum_ fills all of the host left vacant by the plasma, and when the season of decay sets in, it forms resting spores which migrate into the rhizoids of the host, so that both plants regenerate together. Wettstein has compared this symbiotic association with that of lichens, and finds the analogy all the more striking in that the membrane of his new alga had become chitinous, which he thinks may be due to organic nutrition. II. LICHEN HYPHAE A. ORIGIN OF HYPHAE Lichen hyphae form the ground tissue of the thallus apart from the gonidia or algal cells. They are septate branched filaments of single cell rows and are colourless or may be tinged by pigments or lichen acids to some shade of yellow, brown or black. They are of fungal nature, and are produced by the mature lichen spore.