78 
Mycologia 
ous authors tends to throw decided doubt upon the value of this 
method of delimiting species in this genus, as practically any 
species of Spermatophyta which is in nature subject to the attacks 
of any Phytophthora is likely under laboratory conditions to be 
more or less severely attacked by almost any other species. 
Indeed some of the hosts recorded for various species of the 
genus are not known to harbor these fungi in nature. It would 
appear, then, that the parasitism of Phytophthora is of such a low 
order that it will not admit of their being differentiated into races 
as are certain of the Uredineae for example. 
Culture Media 
Such a discussion as the present would scarcely be complete 
without a brief mention of the methods and media employed in 
the pure culture work discussed above. Some of these media are 
very simple in their nature, but often serving an important pur- 
pose in the life history studies on these fungi. Such media are 
vegetable plugs of various kinds, decoctions of fruits and even of 
peaty soil, and in the case of one investigator flies were used in 
distilled water. 
The best success has been obtained from growing these fungi 
on agar made with grain or leguminous seeds as its chief food 
base. Of these peas, beans and oats have proven most efficient 
and satisfactory. Such culture media may be made by the 
following formula, the various seeds and grains remaining con- 
stant. Ground beans 40 grams, agar 15 grams, water 1 liter. 
Prepare in double boiler, or in the autoclave, filtering through ab- 
sorbent cotton. In case of oats it is preferable to boil 100 grams 
of ground oats in a liter of water using a double boiler and cook- 
ing the oats for two or three hours. Strain and add the other 
ingredients and sterilize. Species of Phytophthora prefer a 
slightly acid medium (-)- 5 to -j- 10 Fuller’s scale). 
Synthetic media have received considerable attention from a 
number of investigators as such media would give a basis of 
accurate physiological observations. So far this does not appear 
to have been over successful. The rather extensive series of 
experiments conducted by him have led Jones to conclude that 
