[Vor. 8 
336 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
certain minor differences exist, but considering the great vari- 
ability of spores, varying percentages of perfect germination, 
regardless of all precautions observed, will undoubtedly occur 
in any medium which is not a strong stimulus for germination. 
Germination at H-ion concentrations approaching more or less 
closely those causing inhibition is frequently irregular, and, in 
such cases the range of germination is usually widest at the pro- 
visional optimum. 
The question of hydrogen-ion concentration relations will no 
doubt assist in the explanation of such problems in parasitism 
as host resistance, the establishment of strains of the parasite, 
etc.; and the varied capacity for germination of fungous spores 
may be found in time to be a suitable criterion for the isolation 
of strains. Nevertheless, the facts indicate that it is unwise to 
say that certain species of fungi or certain strains of fungi always 
germinate exclusively within a definite range of hydrogen-ion 
concentration. The limiting hydrogen-ion concentration of a 
fungus, as determined by germination, should be defined in terms 
of composition of the medium, and unless this is done—together 
with a consideration of other related factors—no classification 
of organisms can be made entirely upon any such basis. 
SUMMARY 
Using spores of the eight organisms, Botrytis cinerea, Aspergillus 
niger, Penicillium cyclopium, P. italicum, Lenzites saepiaria, 
Puccinia graminis, Fusarium sp., and Colletotrichum Gossypii, 
a comparative study has been made dealing with the effects of 
the hydrogen and hydroxyl-ion concentration upon germination 
in solutions of mannite, peptone, Czapek’s full nutrient, sugar 
beet decoction, ‘water H,PO, and NaOH” and “water HCl or 
KOH.” Under the conditions described and as far as the 
experiments have gone, the following features of particular 
interest may be enumerated: 
(1) Germination is a process which is strikingly supported 
by conditions of active acidity; relatively low percentages of 
germination, in most cases, are obtained under conditions of 
active alkalinity; and nutrition exerts a pronounced influence 
upon the relations of spore germination to the reaction of the 
medium. 
