THE GERMINATION PROCESS 389 



by measurements of germ tube growth. Infection of a plant by a path- 

 ogen is dependent usually on at least some extension of the germ tube; 

 if this process is more sensitive to unfavorable conditions than is total 

 germination, a false picture of the potentialities of the organism will 

 be deduced from observations on total germination alone. Unfortu- 

 nately, germ tube measurements are rather more laborious and are 

 perhaps avoided for that reason; a rapid, semi-automatic method of 

 determining germ tube lengths should not be beyond the capacity of 

 modern instrumentation and would be a real contribution to the study 

 of fungi. 



2. THE GERMINATION PROCESS 



Just as we have had to lump together the various morphological 

 types of fungus spore, it is also necessary, with some exceptions, to 

 consider the several germination types as if they were all alike. Of 

 these, the most common and the most frequently studied is formation 

 of one or more germ tubes which grow indeterminately and develop 

 into a mycelium in culture or in a parasitized plant or animal. Among 

 the phycomycetes several types of spore germinate by the formation of 

 smaller endogenous spores, i.e., the parent structure is functionally a 

 sporangium. In Phytophthora injestans the same structure — perhaps 

 best called a conidiosporangium — germinates either by a tube or by 

 formation of swarmspores, depending upon the environment, particu- 

 larly temperature, and perhaps on the age and previous history of the 

 structure (19, 63, 279, 291). The chlamydospores of the smut fungi 

 germinate somewhat differently under different external conditions of 

 temperature (140), concentration (132), and nutrients (264). Basidio- 

 spores of Rhizoctonia solarii form secondary spores on water agar, germ 

 tubes on a nutrient agar (131). The macroconidium of Tliielaviopsis 

 paradoxa similarly germinates very differently on water and on nutri- 

 ent agar (149). 



Multicellular spores often germinate by the simultaneous formation 

 of two or more germ tubes (179); in Pestalotia spp., however, the basal 

 cell normally gives rise to the germ tube (300), and germination in 

 Helminthosporium sativum may be either polar or bipolar (137). 



Conidia of the higher fungi may have one, two, or several nuclei at 

 the time of their formation; a few examples may be cited: 



1. Predominantly uninucleate: Aspergillus spp. (8, 12), Colic tot ri- 

 chum destructivum (49), Trichoderma viride (12), Verticillium albo- 

 atrum (128). 



