214 GERMINATION OF SPORES 



HEREDITARY FACTORS AND GERMINATION 



Many observations on the maturity, longevity, dormancy, and 

 vitality of spores as factors in germination have been recorded, 

 but very little of a fundamental nature is known regarding them. 

 In general, conidia are capable of germination as soon as they are 

 abstricted from the parent cell, just as many seeds may be germi- 

 nated as soon as they are mature. The zygospores and oospores 

 of Phycomvcetes, the chlamvdospores of many smuts, and the 

 teliospores of certain species of rusts, however, are known to re- 

 quire a period of dormancy, which, as in seeds, is characterized by 

 thick, hard, protective walls that are presumably quite impervious 

 to water and oxygen. 



It may well be that some spores must undergo a period of after- 

 ripening also, as has been reported in connection with Ustilago 

 longissima, U. striaeformis, Urocystis anemones, and U. cepnlae. 

 Davis (1924) stored spores of U. striaeformis in the laboratory in 

 a damp atmosphere at 20° C for about 240 days before he could 

 secure germination. About 265 days were required if the material 

 was stored out of doors. Davis was able to hasten after-ripening 

 by exposing fresh smut spores to fumes of chloroform for 1 min- 

 ute, then submerging them for 5 minutes in a 10° £ solution of 

 citric acid, and washing them before placing them in storage. 



The oospores of certain Peronosporaceae, for example, Plasmo- 

 para viticola and Sclerospora graminicola, and the teliospores of 

 certain rusts that normally hibernate and then germinate in spring 

 may be induced to germinate during the preceding autumn. By 

 floating teliospores on water or by alternate wetting and drying, 

 Maneval ( 1922 ) was able to secure germination during November 

 and December. As the season advanced, there was a marked 

 increase in the percentage germination and a decrease in the time 

 necessary for germination to begin. He used Puccinia asparagi, P. 

 helianthi, P. menthae, P. peridermiospora, P. riielliae, P. sorghi, P. 

 sydowiana, P. windsoriae, and Phragmidium potentillae. Still 

 other species appear completely to lack a more or less fixed period 

 of dormancy. Spaulding and Rathbun-Gravatt (1925) noted that 

 under outdoor conditions one collection of teliospores of Cvonav- 

 tium ri hi cola from Ribes rotundifolium retained longevity for 19 

 days, and one from jR. nigrum for 87 days, and that urediniospores 





