270 
Brown . — On the Germination and Growth of 
This method of measurement was, however, somewhat laborious and 
ill suited to the needs of the problem. Apart from the practical difficulty 
of carrying out the measurements sufficiently rapidly so as not to interfere 
too seriously with the various conditions of the experiment, there is the 
fundamental objection that the method of counting is severely restricted to 
the early phases of germination. When the average germ-tube reached 
a length of about ten divisions on the scale used, the method was no longer 
available except at the expense of excessive labour. It was therefore 
discarded in favour of the following one, which was much simpler to carry 
out and which at the same time gave results of much wider applicability 
and probably of more interest from the practical point of view. 
B. Grozvth of Fungal Colonies at different Temperatures and in different 
Concentrations of Carbon Dioxide. 
In these experiments plates of sterile medium, solidified with agar or 
gelatine, were ‘ poured 5 and inoculated at the centre with the fungus to be 
examined. In the case of Sphaeropsis malorum , the inocula consisted of 
mycelium only, as this fungus was found to sporulate very sparingly. For 
all the other fungi spore inoculations were in general used. It may be 
remarked here that, apart from a certain small difference in the amount of 
growth during the early stages, spore inocula and mycelial inocula gave 
rise to colonies of very similar appearance and rate of growth. The 
diameter of the colonies was measured directly by means of a small metric 
scale, and each measurement was made to the nearest half-millimetre. 
As this method is extensively used in a paper dealing with the growth 
of fungal colonies under various conditions which will shortly appear, 
a detailed criticism of it will not be attempted here, but will be reserved 
till that occasion. The procedure is as follows : The plates, which contain 
a somewhat deep layer of medium (on the average, 1 cm.), are inoculated 
at the centre, care being taken to make the original inoculations as local 
as possible. They are then placed, face downwards and with lids off, in 
moist containers, four being placed in each of the latter. The Petri dishes 
are piled in column and separated from each other by means of wooden 
rods in such a way as to allow free access of the air of the container to the 
surface of each. For each temperature examined a comparison was made 
of the rate of growth in air, in air containing 10 per cent. C 0 2 , and in air 
containing 20 per cent. C 0 2 . The contents of each container were analysed 
for its carbon dioxide content at the time of measurement, this being 
especially necessary in the present series of experiments as the C 0 2 content 
of each vessel tended to increase on account of the respiration of the fungal 
colonies within. This effect was negligible in the initial stages of each 
experiment, but became more pronounced as time went on, especially at 
the higher temperatures. It was desirable not to make the measurements 
