364 REPRODUCTION 



peratures (79), and the effect of temperature on the morphology of 

 the conidial fructification in Aspergillus janas (239). 



3. WATER. RELATIONS 



Satisfactorily quantitative determinations of the moisture require- 

 ments of sporulation are rare. Indications are, however, that specific 

 fungi have specific requirements. At one extreme, Colletotrichum 

 lindemuthianum and other anthracnose fungi sporulate much more 

 profusely at high than at low humidity (318). Conidiation in Sclero- 

 spora spp. (306, 307) and in Peronospora destructor (317) is also fa- 

 vored by high humidity. The formation of sexual structures in asco- 

 mycetes and basidiomycetes (10, 111, 283) and sporangium formation 

 in Sporodinia grandis (147) are believed to proceed more rapidly at 

 high than at low moisture levels. 



Somewhat lower humidities are tolerated, but are not necessarily re- 

 quired, by some of the rust fungi (318), by Botrytis cinerea (140), and 

 by Bremia lactucae (228). Species of Alternaria in culture sporulate 

 rather better if the culture is allowed to dry out (90, 233). Finally, 

 the powdery mildew fungi appear to be relatively independent of hu- 

 midity or possibly favored in both sexual and asexual reproduction by 

 lower atmospheric moisture (47, 125, 318). Asci of Erysiphe graminis 

 are reported to form only if the perithecium is alternately wetted and 

 dried (76), but it seems doubtful that this is a general requirement 

 among the powdery mildew fungi. 



The weight of evidence favors the generalization that reproductive 

 processes, in most fungi at least, are favored by moderate rather than 

 high atmospheric humidity. However, one may see from even a super- 

 ficial glance at the original work that accurate control of the environ- 

 ment and quantitative determination of the intensity of sporulation 

 have not usually been achieved. 



Different spore forms of a single species occasionally show different 

 humidity responses; examples include the two asexual spore forms of 

 Choanephora cucurbitarum (19) and the zygote and sporangium of 

 Sporodinia grandis (13, 172, 247). 



Miscellaneous reported effects of atmospheric humidity include 

 negative hydrotropism of sporangiophores (172, 300), transitory ac- 

 celeration of the growth of sporangiophores of Phycomyces nitens at 

 high humidity (300), and changes in the size or morphology of co- 

 nidia (98, 119) and sporophores (39). 



Spore discharge in fungi has been studied in some detail; the sum- 



