56 PHYSIOLOGICAL RELATIONS 



experiments. Conidia, aecidiospores, and uredospores ordinarily 

 germinate best immediately after maturity ; but oospores and 

 teleutospores generally require a period of rest. It is certain that 

 a few saprophytic fungi may also germinate in distilled water. 

 This is true of CEdocephalum albidum, some species of Botrytis, 

 and certain hyaline-spored Basidiomycetes. 



In general, the saprophytic fungi seem to require a nutrient 

 medium for germination ; and the percentage of germination de- 

 pends largely upon the direct food value of the medium, the per- 

 fect food affording the best germination. This is particularly true 

 for Penicillium, Aspergillus, certain Mucoraceae, and probably 

 many other fungi. Moreover, plant pathologists generally recog- 

 nize that most of the imperfect or ascomycetous parasitic fungi 

 germinate most readily in nutrient solutions. Certain of these 

 fungi germinate best in infusions or decoctions of the host plant. 

 Excellent germination may occur in a solution containing a single 

 nutrient, as in sugar solution, glycerin, a nutrient salt, etc. Such 

 cases may, perhaps, justly be classed among food stimuli. 



It is known that many parasitic phanerogams require a special 

 stimulus of the host plant before germination may be incited, and it 

 is reasonable to believe that similar instances will be found among 

 the fungi. According to De Bary, the hoof and feather fungus, 

 Onygena corvina, requires such a stimulus. Very little special work 

 has been done along this line of inquiry, and interesting results 

 may be expected, particularly with species which have thus far 

 proved refractory under the usual methods of culture. Miss Fergu- 

 son has determined that while Agaricus campestris may germinate 

 more or less erratically in many nutrient media, or with special stim- 

 uli, the best and most constant germination yet secured is obtained 

 by placing in the culture drop a few strands of the growing hyphae 

 of the same fungus. In such cases, as a rule, a germ tube of a length 

 not greatly exceeding the diameter of the spore is emitted, but no 

 further growth results unless the spores are transferred. This 

 stimulation occurs whether the medium employed is a nutrient 

 solution or distilled water. These results I have been able to con- 

 firm repeatedly. Moreover, I have found that a similar stimulus 

 to germination is afforded by placing in the culture drop a frag- 

 ment of the fresh tissue of the sporophore. The latter is able to 



