GERMINATION AND GROWTH. 157 
ium of P. infestans, which never fructifies there as long as the 
skin of the tuber is intact. But when, in cutting the tuber, the 
parenchyma occupied by the mycelium is exposed to the contact 
of the air, it covers itself with conidia-bearing branches at the 
end of from twenty-four to forty-cight hours. Analogous results 
are obtained with the stalks of the potato. It is evident that 
in these experiments nothing is changed except the contact of 
the air; the specific conditions particularly remain the same. 
It appears, therefore, that it is this contact alone which deter- 
mines generally the production of the conidiiferous branches.* 
The mode of germination and development in the Mucors has 
been studied by several observers, but most recently by Van 
Tieghem and Le Monnier.f In one of the common forms, the 
Mucor phycomyces of some authors, and the Phycomyces nitens 
of others, the process is given in detail. In this species germi- 
nation will not take place in ordinary water, but it readily takes 
place in orange juice and other media. The spore loses colour, 
swells, and absorbs fluid around it until double its original size 
and ovoid. Then a thick thread is emitted from one or both 
extremities, which elongates and becomes branched in a pinnate 
manner. Sometimes the exospore is ruptured and detached 
loosely from the germinating spore. After about forty-eight 
hours from the first sowing, the mycelium will send branches 
into the air, which again become abundantly branched; other 
short submerged branches will also remain simple, or have tuft- 
like ramifications, each terminating in a point, so as to bristle 
with spiny hairs. In two or three days abruptly swollen 
branches, of a club shape, will make their appearance on the 
threads both in the air and in the fluid. Sometimes these 
branches are prolonged into an equal number of sporangia- 
bearing threads, but most frequently they divide first at their 
swollen summits into numerous branches, of which usually one, 
* De Bary, ‘‘Champignons parasitiques,” in ‘‘ Annales des Sci. Nat.” (4me 
sér.), xx p. 53 Cooke, ‘‘ Microscopic Fungi,” cap. xi. p. 138 ; ‘‘ Popular Science 
Review,” iii, 193 (1864). 
+ Van Tieghem and Le Monnier, ‘‘ Researches on Mucorini,” in ‘‘ Ann. des 
Sci. Nat.” (1873), xvii. p. 261; Summary in ‘‘ Quart. Journ. Micro. Science” 
(2nd ser.), xiv. p. 49. 
