Fungi on Culture edict. 109 
tions, the cultures were grown side by side in diffuse light at the general 
laboratory temperature. 
The method of studying growth by increase of diameter offers certain 
contrasts with that of dry-weight measurements. A comparison of the two 
methods may conveniently be given here. 
As regards simplicity the former has obviously great advantages. 
Thus it is possible to carry out experiments on a large scale, a circumstance 
which allows of abundant repetition of experiment and effective control in 
each case. There is, further, the very great advantage that the growth of 
any one colony can be followed throughout all its stages, whereas the dry- 
weight method involves the destruction of a culture for each measurement 
taken. 
A second point of comparison is that the method of linear measure¬ 
ment is suited to growths on solid media (agar, gelatine, &c.), while the 
method of weight measurement can only be carried out effectively in the 
case of cultures in liquid media. It is certainly possible to determine the 
dry weight of a culture on gelatine media by dissolving away the latter 
with gentle heat, a process which can be carried out without killing the 
fungal mycelium, and thus without appreciable loss of cell contents. A 
similar method is not available for the case of agar media, and if it could be 
shown that reliable figures were obtainable by taking the dry weight of the 
killed (and presumably extracted) fungal mycelium after removal of the 
agar by high temperature, the fact remains that that method would be 
extremely laborious. This circumstance is unfortunate, as agar is in general 
a much more suitable solid medium than gelatine, partly by reason of con¬ 
venience, but especially on account of the fact that gelatine is broken down 
by many fungi, and for that reason cannot be used in experiments where 
relations between growth and nutrition are being tested. Thus the method 
of dry-weight measurement, though well suited to the study of, for example, 
yeasts and such fungi as normally live in a liquid substrate, is not well 
adapted to the conditions under which fungi are generally grown and 
studied in the laboratory, viz. on solid media. Moreover, it should be 
noted that the method of studying the growth in terms of the spread of 
a colony from its point of inoculation is more calculated to throw light on 
some important problems, such as the spread of a parasitic organism from 
its point of infection over the host tissue, than is likely from studies by the 
dry-weight method. In the latter case the conditions are essentially 
different, involving as they do the simultaneous development of a large 
number of colonies in the medium with mutual interference from the start. 
The greatest objection to the method of linear measurement is that it 
affords in many cases no indication whatever of the amount of mycelium 
in the fungal colony. Thus two colonies of the same diameter may 
possess vastly different amounts of mycelium, a fact which may be readily 
