46 



MEMOIRS OF THE >'E\V YORK ROTAXK'AL GARDEN 



This species is characterized by the long, smooth, rigid fila- 

 ments, due to the nature of the sheath. The sheath seems to per- 

 sist for some time after the death and decay of the trichome. 



Plectonema spirale sp. nov. 



Filaments attached at one end, erect and jjarallel, 125-150 m 

 long, variable in width at different periods of growth and in dif- 

 ferent parts of the filaments, when young tapering gradually 

 towards the apices, later bulging in tjie middle and toward the 

 base on account of the coiling and contortion of the trichomes, 

 increasing the length of the diameter 2-3 times ; trichomes 3^ n 

 diam., tapering at the apices; cells quadrate to mostly one-half 

 the diameter, long, pale aeruginous, homogeneous ; cross-walls 

 distinct below, obscure above ; sheath very thin, about 0.5 m 

 diam., hj^aline ; branching simple or geminate. 



Growing on an old pump, forming a dense velvety stratum, 

 with other Myxophyceae, Maricao, no. 1276 h, type. 



It was somewhat troublesome to place this species of Plec- 

 tonema. The attached and erect habit is unusual in the small 

 species, as are also the tapering filaments, although Gomont's 

 description provides for that character. The plants are firmly 

 attached at their bases by thin gelatinous walls, stand very 

 closely together, and are chiefly parallel. In the lower half or 

 quarter of the filament the trichome seems to begin to divide 

 actively, and, not being able to push the uj^per part forward, 

 begins to form a more or less regular to distorted sjjiral, at the 

 same time the sheath enlarges instead of rupturing. Nearly the 

 whole lower part of the trichome becomes thus transformed. 

 The trichome also enlarges somewhat in diameter in the coiled 

 part. Brandling was observed to take place usually in the upper 

 part of the coil or just above. Eventually the coiled portion of 

 the trichome breaks into small segments, which become more or 

 less spherical. "Whether this is a natural process of decay or 

 represents gonidia could not be ascertained. The sheath finally 

 dissolves, but no evidence was at hand to indicate that the frag- 

 ments of the trichome germinated to form new filaments. The 

 jDresence of these bodies in the lower part of the erect tapering 

 filaments suggests the genus Leptochaete. The gonidia in that 

 genus, however, begin to form at the basal cells first, and no 

 coiling of the filaments is known to occur. Again, Leptochaete 



