538 Chaudhuri.—A Study of the Growth m 
Coon’s normal medium agar being employed. In twenty days’ time the 
total growths were as follows : 
In medium 6 mm. thick . . Diameter of mycelial area 80 mm. 
In ,, 12 ,, j) .3 do mm. 
The rings were more closely packed in the thicker medium (Fig. 4). 
Summary. 
Verticillium albo-atrum , B. et R., grows on a large variety of media, 
and always renders the medium alkaline. 
The asparagin of Coon's medium can be markedly reduced without 
much affecting the growth of the fungus; on the other hand, reduction in 
the concentration of the maltose in the medium markedly reduces the 
growth. 
The optimum temperature for growth is 22-5° C., the maximum 30° C., 
and the minimum io°C. 
Aeration in liquid media markedly increases not only the rate of growth 
but also the total amount of growth in a given volume of medium. 
Aeration appears to increase growth by reducing the production of 
waste products, rather than by removing (oxidizing?) waste products 
already formed. 
The rate of surface ‘ spread ' of a culture on a solid medium was com¬ 
pared with the rate of increase of material as measured by dry-weight pro¬ 
duction. The rate of 4 spread ’ as a measure of actual production of fungal 
material was found to be extremely untrustworthy. It gives, however, 
a satisfactory measure of the effect of different temperatures on the rate 
of growth in a medium of constant composition and constant thickness. 
When, however, different media are concerned the same rate of surface 
spread may be associated with extremely different rates of mycelium pro¬ 
duction. 
In surface ‘ spread ’ the fungus follows approximately the compound 
interest law, but the dry-weight production there is more nearly a linear 
relation of time. 
For cultures on solid media in the dark, zonation is confined to a tem¬ 
perature of about 25°C.; there is no zonation at 24 0 C. or 26° C. In the 
light, however, such cultures will show zonation at about 23 0 C. 
The zones are more closely packed in a culture on a thick layer of 
medium than in that on a thin layer. 
There is no evidence that accumulation of waste products in any way 
favours zone formation. 
In conclusion the writer wishes to thank for his valuable help Pro¬ 
fessor V. H. Blackman, at whose suggestion this work was undertaken. 
