REPRODUCTIVE CELLS. 147 



each basidium ; the fructification may be a closed structure, as 

 in the TrufHe, or Puff-ball, and the spores here originate in 

 special hyphal filaments or asci (Gasteromycetes). 



In the lower fungi {Zygomycetes and Oomycetes), at times, a 

 sexual mode of reproduction occurs, in that two similar hyphee 

 approach one another and meet by their somewhat club-shaped 

 extremities. Fusion of the adjacent cells then occurs, and the 

 resulting body puts on a thick pigmented wall, and is known as 

 & zygospore. In a few cases (Eurotium) two somewhat dis- 

 similar organs may be produced from adjacent iilaments. Thus, 

 a large globular organ containing cytoplasm may arise, corre- 

 sponding to an oogomum, and this is fertilised by the content 

 of a smaller organ ( = antheridium) which has arisen close by or 

 from the same hyphal filament just below. The resulting mass 

 then becomes an oospore, and can reproduce the fungus, the 

 fertilised mass often forming swarmspores, which are freed later 

 ou by the rupture of the oogonium, each being capable of 

 forming a hyphal filament, the promycelium. 



In the Schizomycetes, or fission-fungi (Bacteria), the only 

 methods of reproduction are the vegetative, by simple fission, 

 and the reproduction by spores. The spores may arise either 

 by the development of large forms (arthrospores) on a main 

 chain of organisms, or by endogenous formation, the spore being 

 formed by the aggregation of the cytoplasm in certain of the 

 members of a colony, and the production of a thick wall round 

 the resulting mass. Eupture of the original wall of the parent- 

 cell then frees the spore thus formed (Bacillus mycoides, Tetanus 

 lacillus, B. anthracis). These few instances will serve to show 

 the great variety of methods of reproduction in the Fungi. 



4. Reproduction in the Algae (Thallophyta). — It is necessary 

 here to take a few well-defined types for study : thus Spirogyra, 

 Fucus, and Vaucheria afford three distinct varieties of sexual 

 reproduction in this group of plants. 



(a) Conjugation in Spirogyra (see Fig. 108, 1, 2, and 3). — 

 This alga has already been seen to possess the ordinary vegeta- 

 tive mode of reproduction, but, in addition, a method known as 

 conjugation sometimes occurs, especially when the surrounding 

 conditions do not favour vegetative reproduction (towards 

 autumn or in colder weather). In conjugation, two similar fila- 

 ments, adjacent and parallel to one another, undergo with regard 



