Culture of VerticiIlium albo-atrum , B. et Br. 523 
Dry-weight determination . The procedure employed in determining 
dry weight is as follows: Weighing bottles with a filter-paper inside were 
placed in a drying oven at 65° C. for twenty-four hours, then cooled in 
a desiccator and weighed carefully to a tenth of a milligram. The liquid 
medium is passed through the filter-papers placed in a funnel, care being 
taken to scrape out any mycelium that might stick to the sides of the flask. 
The filtrate is then washed in distilled water, and placed in the weighing 
bottle and put in the drying oven at 65° C. for three days. The bottles 
are then placed in a desiccator and the weights determined. The difference 
is taken as the actual weight of mycelium produced. 
In the case of an agar medium, the portion over which the fungus has 
spread out is carefully cut out and placed in a test-tube, with distilled 
water, which is boiled to melt the agar ; the whole is then passed through 
the filter. Washing in this case is done with boiling distilled water three or 
four times. After that the material is dried and weighed as before. 
The washing, especially with hot water, no doubt dissolves away 
a certain portion of the dry matter, but the amount so lost is slight, and is 
probably roughly proportional to the original mass of material. 
Growth and Temperature. 
Effect of temperature. The fungus grows very well both in darkness 
and light at room temperature in summer (i 8°-2 o° C.), whereas in winter 
little or no growth takes place at room temperature. Series of cultures in 
various media were grown at different temperatures, viz. 5 0 , io°, 12 0 ,14 0 ,16°, 
18°, 20 0 , 21 0 , 22*5°, 24°, 25 0 , 27 0 , and 33 0 C. It is found that the best growth 
takes place at 22-5° C. No growth took place in cultures incubated at 33 0 C. 
fora week, and when removed to 22-5° C. such cultures showed no growth ; 
apparently the fungus had been killed or lost the power of germination. 
No growth took place in a week at 5 0 C., but when transferred to 22-5° C. 
the growth of such cultures was very vigorous. Even at io° C. no apparent 
growth took place. Above that, growth begins, reaching its optimum at 
22-5° C. At 25 0 C. the growth is less, and at 27 0 C. there is no growth. 
Fig. 3 represents graphically the growth at different temperatures, 
determined first by measurement of the diameters of colonies after fifteen 
days, secondly by measuring the length of the germ tubes in hanging drops 
of distilled water after twenty-four hours. In measuring the length of the 
germ tube, all the tubes from a single spore were counted. 
The two curves are very similar and have their optimum at 22-5° C. 
The difference lies in their maximum, for many spores produced short germ 
tubes at 27 °C. in hanging drops, whereas when examining the agar medium 
of Coon’s normal solution, no visible growth was found after fifteen days, 
though the spores remain living, for at a lower temperature a mycelium 
soon appears. 
