318 Brown .— Studies in the Physiology of Parasitism . /. 
recommend it for use in such an investigation as it was intended to 
prosecute. This anticipation has not been disappointed. It was found 
possible to obtain from young recently germinated spores of Botrytis an 
extract much more powerful than any hitherto attained, and furthermore 
a method has been elaborated for obtaining such material in fairly large 
quantities without prohibitive labour. As the method, though containing 
nothing new in principle, is novel, insomuch as no such procedure has 
hitherto been attempted, and as it may be found to be applicable to other 
studies along similar lines, it will be described in some detail. 
C. Preparation of Standard Extract. 
As it was thought advisable to use the same strain of fungus throughout, 
certain cultural precautions were taken in order to retain its vigour, and 
more especially its capacity for spore production. Up to the present time 
two primary cultures of Botrytis cinerea have been employed, one in the 
earlier stages, the other throughout the remainder and greater part of the 
investigation. 1 The former strain ceased after a few months to produce 
spores in abundance, and no treatment, such as alteration of temperature or 
of medium, was effective in restoring it to its original freely sporing con¬ 
dition. Up to this stage the practice had been to reculture the stock 
cultures rather frequently—once a fortnight—and to incubate them at 25 0 C. 
With the new culture this procedure was modified, stock cultures being 
kept at laboratory temperature (about 20° C.), and only undergoing 
reculture at much longer intervals—actually once in about three months. 
The present strain has now been in culture in this laboratory for a year and 
a half, in which time it has reached its sixth generation, and it still spores 
as freely as ever. Stock cultures are made in large ‘ boiling tubes 5 on the 
potato agar medium to be described below. 
The first object is to provide an abundant supply of spores. This is 
done by the usual Petri-dish method, the culture medium being inoculated 
with the spores prior to pouring in order to obtain uniformity of development 
over the plate. As culture media, trials were made of turnip, prune, and 
potato agars. P'rom the point of view of copious spore formation, the last 
is incomparably the best, and it has accordingly been employed throughout. 
It has the following composition : 
Peeled potato ...... 200 grs. 
Agar ....... 10 grs. 
Water . . . . . . to 1 litre. 
The potatoes are boiled in water till they form a mush, which after 
cooling is pressed through a muslin bag in order to break down the larger 
1 Both cultures were obtained from the 1 Centralstelle fur Pilzkulturen Amsterdam. 
