MATURATION AND DORMANCY 397 



The ascospores of many ascomycetes, particularly but not exclusively 

 coprophilic forms, exhibit a pronounced dormancy which is broken by 

 brief exposure to high temperature (69, 120, 121, 122, 123, 139, 251). 

 Rather intensive study of ascospore dormancy in Neurospora spp. has 

 revealed several features of the phenomenon: 



1. Activation — breaking of dormancy — is reversible, i.e., activated 

 ascospores become dormant again if prevented from germinating (107). 



2. Activated ascospores decarboxylate pyruvic acid and respire vig- 

 orously; dormant spores respire slowly (Figure 2) and do not decarbox- 

 ylate pyruvate (108, 110). 



3. Furfural and related unsaturated heterocyclic compounds activate 

 fresh ascospores (79, 272, 273). Aged dormant spores are activated by 

 furfural only if they are first heated (275). 



Emerson (80) proposes that furfural duplicates the action of a nat- 

 ural catalyst which is normally induced to form or to become active by 

 the heat treatment. It is of course equally possible that a natural in- 

 hibitor is present in fresh spores and is inactivated by heat or by those 

 chemicals which induce germination. 



Neither permeability to water nor to gases can be invoked as a factor 

 in ascospore dormancy in Neurospora tetrasperma (107, 170). How- 

 ever, the activating effect of alkali on ascospores of Ascobolus spp. (318) 

 may implicate permeability to water, and dormant ascospores of N. 

 tetrasperma are relatively impermeable to cations (169a). 



Sporangiospores of Phycomyces blakesleeanus are activated by a heat 

 treatment, e.g., 15 minutes at 50°C (232). The effect is duplicated by 

 hypoxanthine. 



Teliospores of the rust fungi normally do not germinate until several 

 months after their formation. Although chemical and moisture treat- 

 ments have been reported to hasten germination (142, 181, 196, 221, 

 280), the same treatments fail in other studies (129, 156). Until sys- 

 tematic analysis has been accomplished, we must assume a long obligate 

 rest period as characteristic in these spores. 



In the life cycle of the smut fungi the chlamydospore is analogous to 

 the teliospore of the rust fungi. Periods of 200 days or more are re- 

 quired for germination to begin in certain races of Ustilago striaejormis 

 (66, 152). The germination of these spores is often much accelerated 

 by chemical treatments (47, 66, 165, 205, 206), by low-temperature soak- 

 ing (136), by high-temperature cultivation of the infected host (152), or 

 by variations in moisture (281). Mechanical abrasion also shortens the 

 dormant period in Ustilago striaejormis (153). 



It is not yet possible to envision a single explanation for all types of 



