78 : BOTANICAL GAZETTE [JANUARY 
65 per cent. sporangia only; below 40 or 42 per cent. the mycelium is sterile, 
But sporangia may be produced in a greater humidity if anything, e ga 
current of air, promotes transpiration. 
When the air pressure is reduced to 40 or 60™™" of mercury partheno- 
genesis results; below 20-25™™ nosex organs are formed, and below 15-20™ 
no sporangia develop. 
In discussing the food supply it is proved that carbohydrates are needed 
to form zygotes, while sporangia may be formed luxuriantly in nitrogenous 
media. 
It is of interest to note that different isomerous compounds may behave 
differently. Thus maltose provides the food needed for zygote production 
while lactose does not. Unfortunately, stereoisomers were not investigated. 
The minimum concentration in which zygotes could be formed was deter- 
mined ; for this was shown to depend upon the concentration rather than 
upon the absolute quantity of food present. -A small quantity of acid salt 
favored zygote building while normal salts and acids retard it. The author 
thinks the favorable substances increase the permeability of the protoplasm 
to nourishment. 
Parthenogenesis in general results when conditions are suited to the pro- 
duction of sex organs and then change so as to restrict their functioning. It 
results with the greatest certainty when the plant grows in a reduced atmos- — 
pheric pressure, e. g., about 50™™, . 
As a result of the work, the view of Brefeld, that the determination of the 
kind of organs to be produced comes from within, must be abandoned. Also 
the prevalent notion that zygotes are made in “hard times” finds little sup- 
port, as in nearly every case their formation is more easily arrested than that — | 
of sporangia. 
Since in luxuriant vegetative growth diminished humidity, permitting trans- 
piration, results in the formation of sporangia, the latter may be regarded as t 
shortened branches rendered fertile by the extra supply of nourishment at 
their disposal, or by some as yet unknown stimulus. 
Sporangia and zygotes are morphologically homologous organs, devel- 
oping from aerial hyphe of the same construction. They are similar phys- 
iologically and can develop only in air. The stimulus which calls them forth 
is transpiration, but the optimum for each lies at a different point; higher me 
sporangia, lower for zygotes. 
The fact that aerial hyphe are subject to a molecular impact different 
from that on the submerged hyphz may be a determining factor in the deve 
opment of reproductive organs. Also the fact that submerged hyphe mé ; 
absorb nourishment osmotically through a great area while an aerial bra 
receives it through a relatively small cross section may account for some | 
the differences between aerial and submerged parts of fungi, and of bight 
plants as well. — F. L. STEvENs. 
cial 
