135 
If a bit of this mycelium was transplanted every third day to a new 
vessel of the pea-extract, it also grew rapidly to a rich mycelium, and 
this was done repeatedly for two and a half years with the same result 
—not a trace of either zoosporangia or oogonia was developed ; the 
mycelium remained completely sterile the whole time. 
Yet at any period during this two and a half years it was only 
necessary to put a bit of the sterile mycelium into tap-water—i.e., to 
suddenly starve it—and in a few hours it developed abundance of 
zoospores, whereas if he put such a piece into Agar (a gelatinous or 
gum-like substance obtained from certain sea-weeds), it immediately 
proceeded to form oogonia. If, again, the well-nourished sterile my- 
celium is put into 1 °/o salt solution, it forms neither zoosporangia 
nor oogonia, but at once developes gemme, i.c., resting bodies con- 
sisting of jointed bits of the mycelium in which the protoplasm 
collects, 
It would take much too long to describe all the experiments, or the 
precautions and proofs which led step by step to these results, but I 
cannot forbear just adding the explanation they give of ordinary ex- 
periences in our laboratories. When I want a stock of Saproleg nia 
for teaching purposes I float a few dead flies, black-beetles or meal- 
worms on water; the dead bodies slowly diffuse peptone-like sub- 
stances into the water and a rich mycelium rapidly radiates out from 
each. As long as the food-material is abundant the mycelium re- 
mains sterile; as the outflow of food-substances diminishes, however, 
owing to the extra demands of the enlarging mycelium, the distal ends 
of the radiating hyphz begin to form zoosporangia in the less nutri- 
tious solution into which they are forcing themselves. As time goes 
on the starvation of the mycelium proceeds further, and now the 
oogonia begin to appear in those hyphz which find too little food for 
zoospore-formation let alone growth. 
Time will not admit of even a recapitulation of similarly decisive 
experiments with Mucor, S porodinia, Eurotium and other Fungi, but 
I may remind you that we proceed quite similarly with the fungus 
Saccharomyces (Yeast). When we want spores for class demonstration 
we simply take well nourished sterile yeast cells, put them on a wet 
Porous porcelain plate, and in z4-48 hours the starved cells begin to 
develope spores. 
One striking experiment with Sporodinia, which developes its 
sporangia in air, not in water. If a strong culture is placed in each 
of two similar vessels, and you keep one covered by a glass plate and 
one open so that the evaporation partially dries the air, the latter 
developes sporangia and the former zygospores. Nay, if the culture 
is large enough and properly disposed, you can keep half the air 
relatively dry by moving the cover-glass so that only part of the culture 
is covered, and in the drier region sporangia will develope and in 
the wetter region zygotes. In this and similar cases the starvation 
necessary to spore-formation is graduated by the transpiration which 
the sporangiophores exhibit. Stop this, and the change in nutrition 
B 
