250 GERMINATION OF SPORES 



at pH 3.80 and sparse germination at pH 8.95 [Ling (1940)]. 

 Tsau^i (1933) secured best germination of oospores of Sclero- 

 spora graminicola at pH 2.9 to 3.1, with very little germination at 

 pH 9.3. Kaufmann (1934) found pH 7.5 optimum for Coprimis 

 mi c ace us, C. comatus, and Cy at hits olla, pH 7.0 optimum for 

 Lepiota cepaestipes, and pH 6.5 optimum for Armillaria mellea. 

 Smart (1937) made a study involving the effect of reaction on the 

 germination of 70 species of slime molds. All species germinated 

 within the range pH 4.0 to 8.0. Full go septic a germinated within 

 the range pH 2.0 to 10, and Fhysarum serpula, pH 2.0 to 8.5. The 

 optimum pH for germination in all species was 4.5 to 7.0. 



INFLUENCE OF OXYGEN ON GERMINATION 



De Bary (1887) noted that spores in a drop of water between 

 the cover glass and slide germinate better near the periphery of 

 the cover glass than near the center. He attributed this effect 

 to the relative amounts of air available. This observation has been 

 verified by everyone who has attempted to repeat the experiment. 

 Dus^ar (1901) gave special consideration to reduced 2 tension 

 as a factor in retarding germination. Blackman (1903) pointed 

 out the occurrence of morphological differences in germination 

 of teliospores in water and in air. Melhus and Durrell (1919) 

 recorded that few urediniospores of Puccima coronata germinate 

 if submerged in comparison with the number germinating if 

 they float at the surface. Abundant evidence shows that a 

 smaller percentage of germination is secured in drops of water 

 containing many spores than in those containing few. Oxygen 

 relations must therefore be considered in studies of spore germi- 

 nation, and they may be expected to be correlated with the ability 

 to become wet and with the specific gravity of the spores. 



The absence of oxygen may not inhibit germination, as is 

 shown by UppaFs (1926) studies on certain Peronosporales. 

 When he removed the oxygen ( by a vacuum pump or by alkaline 

 solutions of pvrogallic acid) from the environment in which 

 sporangia of Phytophthora colocasiae, P. infestans, P. parasitica, 

 and P. pahmvora were placed for germination, these species germi- 

 nated by formation of swarm spores. On the other hand, Albugo 

 Candida, Flasmopara viticola, and Sclerospora graminicola, which 

 germinate in the same manner, require the presence of oxygen 



