SECT. I 



CRYPTOGAMS 



349 



Growth results from the division and elongation of the cells in one direction 

 only. Each cell has a large nucleus and one or several spiral green band-like 

 chromatophores (Fig. 263, C). The cells of Zygncma contain two star-shaped 

 chroraatophores. 



Conjugation, in the case of Spirogyra, is preceded by the development of 

 converging lateral processes from the cells of adjacent filaments. When two 

 processes from opposite cells meet (Fig. 263, A), their walls become absorbed at 

 the point of contact, and the whole protoplasmic contents of one cell, after 

 contracting from the cell wall, passes through the canal which is thus formed 

 into the opposite cell. The protoplasm and nuclei of the conjugating protoplasts 

 then fuse together while the chloroplasts do not unite, but tliose of the entering 

 protoplast disorganise. The resulting cell forms the zygospore invested with a 



Fill. -263.— .4, Conjugation ot Spirogyra quinina (x 240). li, Spirogyra longata(x 150) ; z, zygospore. 

 C, Cell of Spirogyixt jugcitis ; li, nucleus ; rh, chromatophores; p, pyfenoid. (x 250.) 



thick wall, and filled with fatty substances and reddish-brown mucilage-spheres. 

 This form of conjugation, which is the one exhibited by most species, is described 

 as scalariform (Fig. 263, A), as distinct from the lateral conjugation of some 

 species, in which two adjacent cells of the same filament conjugate by the 

 development of coalescing processes, which are formed near their transverse wall 

 (Fig. 263, B). In some genera the zygote is formed midway in the conjugation tube. 

 The conjugation nucleus of the young zygospore gives rise, according to 

 Chmielewsky, to four by two successive divisions. According to Karsten this 

 is to be regarded as a reduction division C*^). On germination the zygote grows 

 into a tubular cell, from which by cell division the filament is derived. 



