536 
ADRIAN J. PIETERS 
does very well when one wants only to say that a food is poor or very 
good, but obviously if the number of oogonia formed is to be used as a 
measure of the value of a food, a more exact method of determining 
that number is necessary. In the present work the method of Klebs 
was used to some extent, especially in the earlier part of the work, 
but it soon became evident that this was not sufficiently accurate. 
When the value of various foods for vegetative growth is to be deter- 
mined, the mycelium is dried and weighed at the conclusion of the 
experiment, but it is not practicable to weigh the oogonia produced; 
these were therefore counted. For this purpose the mycelium was 
removed from the dish in which it was growing and laid on the inside 
of a Petri dish cover. Here it was carefully spread out by means of a 
jet of water from a pipette till it lay as a circular flat mass, the older, 
and thicker, portion at one end or near the middle and the younger 
portions forming a fringe around this. 
Fig. I. Diagram showing the arrangement of the spaces in which the oogonia 
were counted. 
The bottom of the Petri dish was then inverted and laid on the 
mycelium, so that the whole lay flat and firm between the two halves 
of the Petri dish. A square ruled micrometer had been fitted to the 
