FORMATION OF CELLS. 



II 



bipartition of the nucleus or nuclei of the cell.] Generally, the number of daughter-cells 

 which arise in this manner is considerable; as an instance may be mentioned the 

 formation of spores in Ascomycetes {Peziza ^), (Fig. 7). The tubular mother-cells of 

 the spores (asci) {a) are at first densely filled with protoplasm, and contain only one 

 small nucleus. [This divides into two, and this process is repeated until eight nuclei 

 are formed:] the protoplasm becomes frothy, and roundish drops of sap make their 

 appearance in it {h, c). The first stage in 

 the formation of the spores is the conden- 

 sation of the protoplasm in the upper part 

 of the ascus, while it remains frothy in the 

 lower part (<?,/). In this case eight spores 

 are always formed in each ascus within the 

 upper dense protoplasm ; /'. e. round each of 

 the eight nuclei an ellipsoidal protoplasm- 

 mass collects {d) ; each consists at first of 

 coarse-grained protoplasm surrounded by a 

 clear space ; a portion of fine-grained pro- 

 toplasm forms the matrix in which the 

 spores are imbedded. Afterwards each 

 spore becomes more sharply defined ; the 

 clear space disappears {e) ; its substance 

 becomes more fine-grained and clearer; 

 and in one of its foci is formed a vacuole, 

 i.e. a transparent drop of fluid. Finally, 

 each spore surrounds itself with a firm 

 membrane, the vacuole disappears, and in 

 the centre is formed a large strongly re- 

 fractive oil-drop, as well as numerous 

 smaller ones. 



An example is atforded by the forma- 

 tion of the oospheres of Achlyo (Fig. 8) 

 of a somewhat different mode of free cell- 

 formation. The protoplasm collects at the 

 end of a hypha or of a branch of one ; the 

 larger end itself swells up into a globular 

 form (^, J3), and, after the formation of a 

 septum (C), becomes an independent cell 

 (the oogonium). [Numerous small nuclei 

 are present in the protoplasm (as in C). 

 The nuclei multiply by bipartition.] The 

 whole protoplasm breaks up into two, 

 three, four, or more parts, which very 

 quickly round themselves off into a per- 

 fectly spherical form ; [in each of these 

 several nuclei are uniformly distributed.] 

 The parts thus formed {e, e in D) contract 

 greatly during their separation, and their 

 protoplasm becomes denser by expulsion 



of water; after they have become fertilised by the antheridial tubes {a, b in Z)), 

 they become invested with a cell-wall, [and the nuclei in each coalesce to constitute 

 the nucleus of the oospore]. 



Fig. 7. — Peziza convexula. 'A vertical section of tlie whole 

 plant (X about 20); h hymeniuin, i.e. the layer in which the 

 spore-sacs (asci) lie; .^the tissue of the Fungus enveloping the 

 hymenium at its edge <7 in a cup-like manner ; at the base of 

 the tissue 5' are delicate rhizoids, which grow between the 

 particles of earth. R a smaller portion of the hymenium ( x 550) ; 

 sh sub-hymenial layer of densely interwoven cell-filaments 

 (hypliae) ; «— ^asci; among them thinner sacs, the paraphyses, 

 in which lie red granules. 



' [Strasburger, Zellbiklung und Zelltheilung, 1880; Schmitz, Sitzber. d. nicderrhein. Ges. zu 

 Bonn, 1879.] 



