1923] 



LEHMAN — POD AND STEM BLIGHT OF SOYBEAN 155 



The results are graphically presented in fig. 10. The solid line 

 correlates germination with the P H value of the spore suspension 

 at the beginning of the test, while the broken curve expresses 

 the relation between the P H value of the uninoculated solution 

 as found 40 hours later. No germination occurred at the hydro- 

 gen-ion concentration represented by Ph 2.2. At Ph 3.1, a 

 germination of 22.3 per cent took place, but the germ tubes were 

 very short, most of them not as long as the spores. One hundred 

 per cent of the spores germinated, producing tubes several times 

 as long as the spore at P H 4.1, 5.3, and 6.1. The percentage of 

 germination decreases slightly at P H 7 and 8, but increases again 

 to a secondary maximum at P H 8.4 and falls again in the more 

 alkaline solutions. Between P H 4.1 and 8.4 the germ tubes are 

 of approximately the same uniform length, but beginning at 

 P H 9.7 they become shorter and at P H 10.0 are markedly shorter 

 than at 8.4 but not yet so short as at P H 3. A germination 

 amounting to 21.6 per cent occurred in distilled water having a 

 P H value of 5.1 but here the germ tubes were very short. Thus, 

 it is seen that much better germination may be obtained in the 

 mineral nutrient used than in distilled water, and that very good 

 germination occurs over a wide range of hydrogen-ion concen- 

 tration. 



Effect of the Reaction of the Substratum on the Growth 



of Mycelium 



That the degree of acidity or alkalinity of the medium pro- 

 foundly influences growth of fungi is a fact attested by numerous 

 recorded observations. In general, growth has been observed 

 to be more marked on the acid side of neutrality, comparatively 

 few of the species studied producing equally favorable or better 

 growth in alkaline media. Omitting all records relating exclus- 

 ively to bacteria and all not definitely stating the reaction in 

 terms of active acidity, a partial account of the observations of 

 other workers bearing on the relation of growth to hydrogen-ion 

 concentration is given below : 



Meacham ('18), growing Lenzites sepiaria, Fomes roseus, 

 Coniophora cerebella, and Merulius lacrymans on synthetic and 



