286 Trow. — Observations on the Biology and 
Relation of growth to temperature. The cultures were 
carried on at first during the summer months, and growth 
and development was, as has been said, very rapid. After a 
lapse of two months fresh cultures were started — in November, 
1899 — and these made very poor growth, and the reproductive 
organs appeared only after the lapse of a considerable time — 
a week or more. A few experiments sufficed to prove that 
this was entirely the result of the low temperature. Potato 
cultures do not produce an appreciable aerial growth at room 
temperature during our winter, so that in the winter months 
the cultures have to be kept growing in the incubator. 
Growth is very good, at its optimum probably, at a tempera- 
ture of 25 0 C. The incubator is maintained at 24 0 C. to 26° C. 
Growth is stopped at about 35 0 C. The optimum, minimum, 
and maximum temperatures have yet to be accurately ascer- 
tained, but we already know enough to realize that the plant 
is adapted for a summer rather than a winter life in our 
climate. This is the more remarkable, as our wet, mild winter 
would appear to furnish it with a very suitable environment. 
Experiments to determine its capacity to vegetate as a 
parasite. From the outset the plant appeared to be a pure 
saprophyte, but as it was of importance for taxonomic pur- 
poses'to determine the point accurately, two sets of experiments 
were ihstituted. In the first , cultures of cress-seedlings were 
raised in sterilized soil in a damp atmosphere under bell jars. 
These were infected with healthy cultures of the Fungus, 
chiefly by laying the cover-glass cultures on or in the soil 
in contact with the plants. These cultures of the Fungus 
were not absolutely pure, and free watering was resorted to, 
as at that time the power of the mycelium to grow in the air 
was not known. No single case of ‘rotting off’ occurred in 
the six experiments instituted. Indeed the cress developed 
quite luxuriantly under these conditions. In the second , cress- 
seedlings were uprooted and laid in water in sterilized Petri 
dishes and cultures of the Fungus added. These cultures 
were to a considerable extent under microscopic control. 
No infection and little growth took place. The cress-seedlings 
