124 SEX IN MICROORGANISMS 



Zygospore Germination 



The red, stellate zygospores of Frotosiphon can be induced to 

 germinate only after a period of some weeks of dormancy (Klebs, 

 1896). According to Nayal (1933), young green zygospores of one 

 strain of Frotosiphon, when formed under moist conditions, may 

 germinate soon after being transferred to fresh media, while older 

 red spores, especially if they have been subjected to heat or desicca- 

 tion, remain dormant for some days before being capable of germina- 

 tion. The zygospores of Folytovia germinate readily under favorable 

 conditions (Pringsheim and Ondratschek, 1939). However, in a 

 depressingly large number of studies on the sexual cycles of unicellu- 

 lar algae, the obstacle of zygospore germination has proved insur- 

 mountable. The walls of such spores are usually relatively thick, and 

 in some species are said to consist of three layers of different composi- 

 tion (Gerloff, 1940). Though actually only 1 to 2 [j. thick, they may 

 achieve a remarkable degree of impermeability to water and chemical 

 agents. Thus zygospores of Chlamydoiiioims vweivmii have been 

 known to survive after several days of immersion in absolute acetone 

 or after 4 years in air, though the zygotes of the related C. eiigametos 

 and those of C. viedia are killed by drying (Moewus, 1933, 1950c; 

 Klebs, 1896). Zygospores of a strain of Frotosiphon, isolated from 

 desert silt, were shown to remain viable after heating at 75° to 91°C 

 for 18 hours, or at 50° to 60° for 15 to 18 days (Nayal, 1933): while 

 spores of Folytovia were found to be capable of germinating after 

 contact with solid COn for 10 minutes, or after four weeks' desicca- 

 tion over CaClo followed by 10 minutes at 75° (Pringsheim and On- 

 dratschek, 1939). In Chlaviydovwnas engametos, Moewus has re- 

 ported (1946, 1950c) genetic variation in the resistance of zygospores 

 to high temperatures and osmotic pressures. 



Within such impenetrable walls, nuclear changes are extremely 

 difficult to follow (Kater, 1929; Zimmermann, 1921) while we know 

 nothing of the underlying metabolic changes associated with the 

 dormant state. In our present profound ignorance, we have to resort 

 to empirical methods for inducing germination, and a number of such 

 studies have been carried out (see Bold, 1942). In CyVmdrocystis, 

 Pringsheim (1919) found that germination of zygospores — even 

 before maturation was complete — could be induced by transferring 

 them to fresh nutrient media. Lerche (1937) achieved a fair degree of 



