316 DoRAN: ON THE GERMINATION OF FUNGOUS SPORES 
The spores were counted by the use of a micrometer disc 
ruled in squares and the help of a tallying register. The micro- 
meter disc ruled in squares is placed in the ocular, the slide 
bearing the drops of water containing spores is placed on the stage 
of the microscope and moved by means of a mechanical stage 
until the outer line on the micrometer disc appears as a tangent 
to the circumference of the drop. The germinating spores 
appearing between the first two lines of the micrometer disc 
are counted, and then the ungerminated spores in this area are 
counted. When one field as limited by the lines on the micro- 
meter disc is counted, the slide is moved enough to bring a new 
field into view for counting. This is continued until a total of 
fifteen hundred to two thousand spores, both germinated and 
ungerminated, have been counted. This necessitates the ex- 
amination of several or many drops. From the count obtained, 
the relative number of spores germinating is figured, germina- 
tion elsewhere being raised proportionately. This accuracy of 
counting is most necessary when the relation between tempera- 
ture and spore germination is being determined. It is not as 
necessary in the case of toxicity tests with fungicides except 
when the differences in toxicity are small. 
RELATION OF THE VIABILITY OF THE SPORE TO ITS AGE 
Maturity—Until the spore has attained a certain age or 
degree of maturity, it cannot germinate. Even before a spore is 
really mature, it can germinate if other conditions are near 
enough to the optimum. For example, the range between the 
minimum and maximum temperature is considerably greater 
for the germination of a mature urediniospore of Puccinia 
Antirrhint than for the germination of an immature uredinio- 
spore of this fungus, collected the first day it breaks through the 
host surface. The immature spore may be prevented from 
germinating by the action of fungicides not of sufficient con- 
centration to prevent the germination of the mature spore. 
A solution containing 0.257 per cent copper sulphate prevents 
the germination of mature spores of Uromyces caryophyllinus.. 
A solution containing only half as much copper sulphate prevents 
the germination of immature spores of this fungus. It should 
be understood that mature and immature spores may not 
differ morphologically. Spores here referred to as immature are - 
so called because when collected young they did not germinate, 
