602 



PATTERNS AND PROBLEMS OF DEVELOPMENT 



adjoining, respectively, distal and proximal walls of the thallus cell (Fig. 

 iS6, B); but the spores in different mother cells of the same filament may 

 differ in axial orientation. Single thallus cells may give rise to more than 

 two spores, even to thirty-two or more microspores. In these cases the 

 spores apparently form at the surface of the cytoplasm adjoining the cell 

 wall, and their axiate patterns seem to be related to the differential from 

 surface to interior of the protoplasm. Very similar spores with two flagella 

 at one pole of an axiate pattern are formed in other green algae, and both 

 or one of the gametes of some algae have similar axiate pattern. They 



> < 



)—< 



B 



Fig. i86, y4-£.— Zoospores of algae. A, zoospore of Ulolhrix; cytoplasmic regions and pig- 

 mented "stigma" indicated; B, two zoospores developing in a thallus cell with axes transverse 

 to thallus axis, parallel and similarly directed (.4 and B, diagrammatic, after Dodel, 1876); 

 C, type of zoospore characteristic of brown algae; D, zoospore of Oedogonium; E, its develop- 

 ment with axis transverse to thallus axis {D and E after Pringsheim, 1858). 



usually develop by repeated divisions of thallus cells, often with forma- 

 tion of a very large number from a single cell. How the axiate pattern 

 originates is an interesting question. In many forms the axes seem to be 

 in all possible directions; certain figures, however, show the flagellate 

 poles of spores lying superficially directed toward the surface of the 

 mother cell,' but in most figures no such relation is evident. An axiate 

 pattern related to, and determined by, directions of mitoses may perhaps 

 become the polar axis of the spore, the polar region of the spindle be- 

 coming apical. 



It is stated that zoospores of this type attach by the colorless flagellate 



' See, e.g., G. M. Smith, 1938, Fig. 59, Codiutn. 



