THE CELL. 



43 



nal I lY, oil the other hand, is of the greatest importance in the veg- 

 etative life of the plant (growth, tissue-formation). 



I. Direct Cell-formation. —The mother-cell, with its entire con- 

 tents, excepting the membrane, takes part in the formation of the 

 daughter-cell. The life of the mother-cell passes directly into that 

 of the daughter-cell. The visible phenomenon connected with this 

 process is the contraction, due to internal forces, of the primordial 

 utricle of the mother-cell, and the subsequent deposition of a new 

 cellulose membrane either while yet within the old membrane or 

 after its escape from the same. The membrane of the mother- 

 cell is destroyed. Example: swarm-spore formation in the alga 

 Stigeoclonium. insigne (studied by Nageli). 



II. Conjugation. — The contents of two externally not dissimilar 

 cells unite to form one new cell. Either the contents of one cell 

 pass into the lumen of the other cell by 

 means of outgrowths from the membrane 

 and after the opening of the contiguous 

 membranous areas, or the contents of both 

 cells unite by moving toward each other and 

 fusing. The united cell-contents are then 

 surrounded by a new membrane. Ex- 

 ample : Spirogyra and similar algae (Fig. 

 23). 



III. Free Cell -formation. — The 

 daughter-cells appear floating in the con- 

 tents of the mother-cell. Small particles 

 are differentiated within the plasmic con- 



"Pir 2R 



tents of the mother-cell and surround (After Berthoici and' Landois.) 

 themselves with a new membrane. This process is, however, con- 

 nected with nuclear division. Example : ascospore-formation in 

 asci of the fungus-group Ascomycetes. In this 

 process the entire plasmic contents of the mother- 

 cell are not utilized (Fig. 24). 



I Y. Meristematic Cell-formation or Cell-for- 

 ination hy Division. — Septa divide the entire 

 contents of the motiier-cell. Four sub-groups are 

 recognizable. 



Fig. 2-t.— Asci with (rt) Splitting up of the plasm with cornplete 

 sr>oTes of Peziza aur- i r ,. 



antia. (After Berthoid membrane-formation. 



and Landois.) (J) Divisiou of the plasm with j?a7'tial mem- 



brane-formation which occurs simultaneously. 



