26 



PROTISTS AND DISEASE 



off by septa, Fig. 3, B, a, o, and Fig. 4, B. The gametangia 

 appear in the evening and are complete next morning. 



The modes of reproduction of Volvocineae and of Hydro- 

 dictyon (the water-net) should be recalled. In the latter the 

 contents of a single cell divide simultaneously into from 

 7,000 to 20,000 zoospores, which join together to form a new 

 net (Bower). A cell of the same organism in its sexual 



FIG. 4. STAGES OF SOME ALGAE AND FUNGI. A, diagram, or, of algal 

 macrozoospore and young plant, and, 6, of conjugation of micro - 

 zoospores and resulting zygote ; B, Vaucheria, empty antheridium, 

 oospore, and antherozoids ; C. conidia of Achlya changing to zoo- 

 spores, b ; germination of oospore ; and ; a, the first form of a zoospore 

 of Saprolegnia, the second being like b ; D, stages in the germination 

 of the resting spore of a cladochytridian, a, end view, b, side view, 

 c, sporangium forming, d, zoospore ; C and D after de Bary. 



phase produces upwards of 30,000 zoospores which conjugate 

 in pairs or greater numbers (van Tieghem). 



The cells of simple green algae, e.g. Pleurococcus, vul- 

 gar is, are arranged in twos, fours, &c., or separately from 

 one another. Pleurococcus shows as green powder on tree- 

 trunks, &c. Its cells have nuclei and chromatophores. In 

 some young algal cells chlorophyll seems to impregnate 



