. A handbook of cryptogamic botany. Cryptogams. CYANOPHYCEM 431 times associated in chains, are formed immediately beneath them. The cell-wall of the resting-spores is often coloured yellow or brown, and is sometimes warty. After a period of rest they germinate by the bursting of the cell-wall and protrusion of the protoplasm. The hormogones are strings of from four to eight or twelve ordinary cells, situated between two heterocysts, which detach themselves from the rest of the filament, escape from their mucilaginous envelope, move about with a creeping motion, then come to rest, and develop
. A handbook of cryptogamic botany. Cryptogams. CYANOPHYCEM 431 times associated in chains, are formed immediately beneath them. The cell-wall of the resting-spores is often coloured yellow or brown, and is sometimes warty. After a period of rest they germinate by the bursting of the cell-wall and protrusion of the protoplasm. The hormogones are strings of from four to eight or twelve ordinary cells, situated between two heterocysts, which detach themselves from the rest of the filament, escape from their mucilaginous envelope, move about with a creeping motion, then come to rest, and develop into new individuals. Bornet describes the motion of the hormogones of Nostoc as a creeping movement along a solid substratum at a rate of i yu (-ooi mm.) per second. After some hours they come to rest, large refringent globules which had previously been formed in the cells disappear, and they assume the appearance of ordinary filaments. Sometimes they. Fig. 360.—AnabtBfia Jlos-agnm Fr. ( x 400). (After Cooke.) Fig. 359.—N. hyalinum Eenn. A^ 'frond' (x 200) ; B^ portion of trichome with heterocyst, c (X 600). (From nature.) invest themselves with a nmcilaginous sheath, and are transformed directly into spores, but usually the filament lengthens, displaying at the same time more or less sinuosity. The heterocysts do not appear at regular intervals. A new filament is thus formed altogether resembling those Tvhich spring directly from the germination of the spores. Once formed, it is subject to intermittent periods of growth, a second genera- tion of spores, with thinner cell-walls, being sometimes formed after the first. In other cases the filament springing directly from a hormogone assumes a zigzag form, in consequence of some of the cells dividing in the transverse, others in the longitudinal direction. In N. muscorum (Ag.) all the cells except the heterocysts are sometimes transformed into spores. The spores will occasionally germinate while still within the ' frond.' The
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