. Comparative morphology and biology of the fungi, mycetozoa and bacteria . Plant morphology; Fungi; Myxomycetes; Bacteriology. CHAPTER VII.—PHENOMENA OF VEGETATION.—LICHENS. 413 Nostoc-colonies attacked by the Lichen-forming Ascomycete. The hyphae of the Fungus intrade between the cell-rows of the Alga, which are strung together like the beads of a rosary interrupted by heterocysts and imbedded in a firm jelly; they branch in a manner which varies according to the species, and determine the general growth of the compound thallus. In most forms numerous peripheral branches of the hyphae run ve
. Comparative morphology and biology of the fungi, mycetozoa and bacteria . Plant morphology; Fungi; Myxomycetes; Bacteriology. CHAPTER VII.—PHENOMENA OF VEGETATION.—LICHENS. 413 Nostoc-colonies attacked by the Lichen-forming Ascomycete. The hyphae of the Fungus intrade between the cell-rows of the Alga, which are strung together like the beads of a rosary interrupted by heterocysts and imbedded in a firm jelly; they branch in a manner which varies according to the species, and determine the general growth of the compound thallus. In most forms numerous peripheral branches of the hyphae run vertically into the surface of the gelatinous colony and end blindly in it. Leptogium, Obryzum and Mallotium (Fig. 179) are exceptions to this, in which the extremities of the peripheral branches pass into a rind or outer membrane, a simple or in places a double layer of polyhedric tubular cells without interstices with pellucid contents and colourless or brown walls, which covers the whole thallus. The membrane of the cells is often stronger on the upper side of the thallus and thickened more on the outer than on the inner side, recalling the epidermis of the higher plants. Numerous multicellular hairs spring from all parts of the cells of the lower s^^^^j^ rind in Mallotium, some- times short and isolated, sometimes longer and united in bundles; they serve to fix the thallus to the substratum. No direct and in- timate connection can be perceived in most species between the branches of the hj'phae and the Smgle fig. 179. Ufattattum HUdibrandU, Garov. a radial longitudinal section through the . 1 11 Tj i iU thallus; w the under side. * portion of a very thin section through the under side showing algal cells. UUl tne Spe- ^jie nnd, halis, hyphae and a magn. 190, b 390 times. cies of Plectopsora and Physma are distinguished by the presence of haustoria, short hyphal branches which grow in the direction of any Nostoc-cells and either lay their conical extremit
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