I IO 
Brown.—Experiments on the Growth of 
visible to the eye though an exact measurement of the difference may be 
difficult to obtain. In fact in many cases there is a direct correlation 
between vigorous marginal growth and scantiness of mycelium within the 
culture. 
But while the method of linear measurement gives in general no indi¬ 
cation of the amount of growth made, it is well to remember that the 
alternative method is not free from objections in this respect. Numerous 
contradictions have arisen in the literature of fungal nutrition from misinter¬ 
pretation of the results of dry-weight experiments. An example will 
suffice to show how errors have arisen. Suppose the object is to compare 
the nutritive value of two substances or two cultural media, A and B, for 
a particular fungus. The simple method is to start the fungus on the two 
media and at the end of an arbitrary time, say a fortnight, determine the dry 
weights of the mycelia produced in each case. Working in this way different 
investigators have come to the most contradictory results. The source of 
the apparent contradiction lies in the fact that the same fungus may have 
a growth-time relationship widely different on different media. In one case 
the increment of growth may be rapid at first and then reach a moderately 
low limiting value : in the other it may slowly increase to a high maximum. 
Again, the curve of dry weight of a fungus does not remain at a steady 
value but again diminishes through degenerative changes. Thus the dry- 
weight method cannot be safely used unless one is prepared to follow the 
growth at short intervals throughout its whole history. Short of that, the 
results v/ill have no value. These considerations greatly increase the laborU 
ousness of the dry-weight method. 
All things considered, one may safely say that the method of linear 
measurement is the best to apply in exploratory work. By this means one 
can indicate problems of limited dimensions to which the more searching 
method of dry-weight determination can profitably be applied. 
There remains the question of the relative accuracy of the two methods. 
The advantages, quite apart from the number of controls that can be em¬ 
ployed, appear to rest with the method of linear measurement. Experience 
in this laboratory has shown that it is difficult to obtain an even curve of 
growth as determined by dry-weight measurement, as irregularities tend to 
appear under apparently identical conditions among the various cultures. 
In linear measurements of growth, the degree of uniformity obtainable 
depends on a variety of factors. With the same fungus, it may vary with 
the medium ; thus it is difficult on some media to get uniform starting of 
the different controls while it is quite easy on others. Again, the degree of 
uniformity varies with the phase of growth of the colony, and it will be 
shown subsequently that the tendency to lack of uniformity among the 
various controls is an indication that staling is taking place. 
As regards the two fungi mainly dealt with in this paper, Sphaeropsis 
