. A handbook of cryptogamic botany. Cryptogams. 436 PROTOPHYTA (Thur.) while still within the sheath, the cell-contents passing from a heterocyst into the basal cell of a hormogone. Multiplication by quiescent resting-spores has been observed in some species of Rivulariaceae. The lower portion of the green part of a fila- ment immediately above the basilar cell is transformed into an elliptical thick-walled spore, which escapes from its investing membrane, and, after a period of rest, either develops directly into a new filament, or breaks up into a number of hormo- gones. The spores of Gloeot
. A handbook of cryptogamic botany. Cryptogams. 436 PROTOPHYTA (Thur.) while still within the sheath, the cell-contents passing from a heterocyst into the basal cell of a hormogone. Multiplication by quiescent resting-spores has been observed in some species of Rivulariaceae. The lower portion of the green part of a fila- ment immediately above the basilar cell is transformed into an elliptical thick-walled spore, which escapes from its investing membrane, and, after a period of rest, either develops directly into a new filament, or breaks up into a number of hormo- gones. The spores of Gloeotrichia punctulata (Thur.) are rough. Under the name 'conids' Bornet and Flahault also describe special propagative cells which become detached from the lower part of the filament. By far the larger number of species of Rivulariacese grow in fresh water, especially stagnant, also on damp soil and on wet rocks. The species of the typical genus Riviilaria Roth are especially abundant in both running and standing water ; R. fluitans (Cohn, Hedwigia, 1878, pp. i and 33) floats free on the water, forming a blue- green scum which enters largely into the composition of what is known as ' flos aquae.' Some species have a red tinge. Calothrix Ag., though placed by Rabenhorst among the Scytonemacese, has all the cha- racteristics of the Rivulariaceae. The filaments of some species are comparatively thick, as much as Q-oi mm. in diameter, and are invested in a copious, often coloured, mucilaginous sheath. Microckcete Thur. is nearly allied to Calothrix, as is Gloeotrichia Ag. to Rivularia. Several species of Rivularia and Calothrix grow in salt or brackish water, and Isactis Thur. is ex- clusively marine. In Hormadis Thur., which is also marine, the fila- ments are curved in a serpentine manner, and this character, together with the interstitial heterocysts, appears to indicate an approach to the Nostocaceae. Other genera included in the Rivulariaceae are Fig. 365.—Isaciisp
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