CELL FORMATION BY UNION. 



47 



masses come in direct contact by means of a tube (the pol- 

 len tube) which touches with its lower extremity the embry- 

 onic vesicle. 



(a) The foregoing classification of the modes of cell-formation differs 

 in many respects from that given by Sachs in the fourth edition of his 

 1 ' Lehrbuch." His classification as there given is as follows : 





Fig. 38. Vaucheria sessUis. A, orisrin of the lateral branches, off {oogoniwm}, and 

 h (anthfridium), from the filament ; B, the branch a (the same as A in A) has its ter- 

 minal portion cut off by a partition ; in og the protoplasm is becoming greatly con- 

 densed ; C. the same as oq of B, but further advanced (now called an oosphere) and 

 the wall burst open, permitting the escape of a drop of mucilage si ; D, small motile 

 cells (spermatozoids) from the terminal cell of a in B ; E, the same as C, but a little 

 later the spermatozoids are entering through the opening ; F, a, the branch a in B, 

 with the terminal cell now empty, on account of the escape of the spermntozoids ; 

 osp, the same as E, and og in B, after union with the Kpermatozoids the protoplasm 

 is surrounded by a thick cell-wall and it is now called an oospore. X 100. After 

 Sachs. 



A. FORMATION OP REPRODUCTIVE CELLS. 



1. Rejuvenescence. ^ 



2. Conjugation. -' 



3. Free Cell -Formation. 



4. Formation of Reproductive Cells by Division, which is made to 

 include the formation of pollen, the spores of mosses and ferus, and 

 the conidia, stylospores, and basidiospores of many fungi. 



