Wager. — The Sexuality of the Fungi. 589 
showed that at a low temperature, 6-7° C. 5 only sterile 
mycelium is formed ; that the ’formation of conidia demands 
free access of air ; and that the formation of zygotes is 
connected with bad conditions of vegetation, such as the 
transport of a prosperous culture into an unfavourable 
medium, dilution of the nutrient medium, or too strong 
a solution of it, or an elevated temperature. 
Klebs 1 showed in his studies on Sporodinia grandis that 
carbohydrates are needed to form zygotes, and that sporangia 
may be formed luxuriantly in nitrogenous media. Increased 
transpiration tends to the formation of sporangia. When 
transpiration is checked within certain limits, zygotes are 
formed in addition, and when still further checked, zygotes 
only are formed. When the air-pressure is reduced partheno- 
genesis results, and if still further reduced no sexual organs 
are formed at all, and ultimately the production of sporangia 
also is stopped. 
Some observations of my own are also interesting as bearing 
upon this point. In the case of Polyphagus , when there is an 
abundant food supply in the form of fresh Euglena cells, 
sporangia only are produced. In a very short time, however, 
as this special food supply becomes exhausted, sexual organs 
are also formed, and in the later stages of a culture, when the 
food supply is much reduced, sexual organs only are formed. 
In Peronospora parasitica and Cystopus Candidas I find that 
oospores are mostly developed in those parts from which the 
food supply has not been absorbed by sporangia, and which 
are still succulent and full of sap. The portion of the stem 
which contains them is large and succulent, with few asexual 
organs present, or they are contained in the young succulent 
tissues at the apex. Those parts of the plant which are 
covered with asexual spores and which appear white — those 
parts where the Fungus is visible to the observer on a cursory 
examination — very rarely contain sexual organs in abundance. 
1 Klebs, Zur Physiologic der Fortpflanzung einiger Pilze. I. Sporodinia grandis . 
Jahrb. f. wiss. Bot., xxxii, 1898. See also II. Saprolegnia mixta. Jahrb. f. 
wiss. Bot., xxxiii, 1899. 
