Tribonemaceas 



413 



and /) ; also by zoogonidia with a pair of unequal cilia and two or more parietal 

 chromatophores (tig. 88 C', fig. 263 C). Either one or two zoogonidia may arise 

 from a single cell ; the inequality of the cilia was first demonstrated by 

 Bohlin ('97). In the escape of the aplanospores and zoogonidia the H -pieces 

 of the cell -wall fall apart, thus causing a dislocation of the filaments. 



Gametes are only rarely produced. They are isogamous although con- 

 jugation is to some extent anisogamous, since it is stated that one gamete 

 comes to rest before the other swarms up to it and fuses with it. 



In Bumilleria the filaments are slender and somewhat delicate, and the 

 cell-wall is not so distinctly built up of H -pieces; neither do the latter 

 exhibit the special structure which is so characteristic of the wall of Tribonema. 

 On the other hand, the filament may possess a by no means insignificant 







Fig. 264. Bumilleria sicula Borzi. A, vegetative filament; B, filament showing cell-division; 

 C, escape of zoogonidia ; D F, germination of zoogonidia ; G, formation of gamete-mother- 

 cells ; H, an isolated gamete-mother-cell; /, formation of gametes; K, gametes; L, fusion 

 of gametes; M, zygospore; Nand 0, germination of zygospore. x about 500. (From Wille, 

 after drawings by Borzi.) 



N.B. The zoogonidia are depicted with only one cilium, but this is probably an error in the 

 original observations. 



mucous sheath, continuous in character and consisting of the pectic con- 

 stituents of the wall. Much investigation is still required concerning the 

 zoogonidia and gametes of this genus. 



The genera are: Tribonema Derbes & Solier, 1856 [ Conferva as denned by Lagerheim, 

 1888] ; Bumilleria Borzi, 1895. For full reasons for the abandonment of the generic name 

 ' Conferva,' consult Hazen ('02) or West (G. S. W., '04). Tribonema bombycina (with its 

 forma minor] is a common Alga in all countries and it occurs in very varied habitats. 



Bumilleria is much less frequent than Tribonema, but is occasionally found in 

 considerable quantity in small ponds. 



