216 GERMINATION OF SPORES 



temperatures between 3° and 11° C, P. triticina remained viable 

 124 days. 



Smut fungi are known to retain their viability for long periods. 

 .McAlpine found Tolyposporium bursum on kangaroo grass viable 

 after 4 years 1 storage in the laboratory. Long ago Brefeld noted 

 that Tilletia tritici, when kept dry in the herbarium for 8% 

 years, was still germinable. Urocystis cepulae is reported to re- 

 main viable in the soil for at least 5 years. Many root-invading 

 pathogens are well known to persist in the soil not only from one 

 year to the next but also for a term of years. 



It has been indicated that, as teliospores of certain rusts become 

 older, less time may be necessary for their germination, especially 

 in species in which the teliospores constitute the overwintering 

 stage. The converse is true in many conidial forms. Brown 

 (1922) observed that 6-week-old conidia of Botrytis cinerea, for 

 instance, require twice as long to germinate as do 10-dav-old ones. 

 On the other hand, a larger percentage of conidia of Phyllosticta 

 solitaria are capable of germination 10 to 14 days after they are 

 of mature size than can germinate immediately after they have 

 attained this size [Burgert (1934)]. It thus appears that an in- 

 terval may exist between morphological and physiological ma- 

 turity of spores. 



The retention of viability by spores is in some instances mated 

 to their separation from the parent cell and from the host tissues 

 and to their isolation from each other. The ascospores of bark- 

 inhabiting and leaf-inhabiting species are known to retain their 

 ability to germinate for a longer time if they remain within the 

 host tissues than if they are removed. Similarly, the conidia of 

 Gloeosporium, Colletotrichum, Lecanosticta, and other genera in 

 which a mucilaginous matrix holds the conidia together in mucoid 

 masses succumb much more quickly after they have been dis- 

 persed by contact with water. Desiccation is undoubtedly the 

 primary cause of loss of viability in such cases. 



The studies by Goddard ( 1935) and Goddard and Smith (1938) 

 constitute an interesting approach to the problem of dormancy 

 in spores. Goddard (1935) induced the dormant ascospores of 

 Xcuvospora tetrasperma to germinate by heating them for a few 

 minutes at temperatures of 50° C or higher. Germination occur- 

 red within 2 or 3 hours if such heat-treated spores were placed 

 in water at room temperature. If the spores were stored under 



