THALLOPHYTES 
fungus that has retained swimming sperms. These sperms are uniciliate, as are 
the zoospores, a fact which suggested the generic name. 
Peronosporales. These are the downy mildews, and they include 
many destructive parasites that live within the tissues of the host, the 
hyphae branching through the intercellular spaces, crowding between 
the cells, and sending haustoria into them. This internal mycelium sends 
sporophores to the surface of the host, and spores are formed by round- 
ing off the tips of the sporophores or their branches. This process of 
cutting off spores is called abstriction, and such spores are called conidia. 
Oogonia and antheridia are formed upon the internal mycelium, and 
fertilization is effected through a 
fertilizing tube. 
This is the one group of Oomy- 
cetes with distinctly aerial habit, 
as in the Zygomycetes ; but the 
forms are heterogamous, and in 
the life history of many of them 
zoospores appear. The promi- 
nent genera are as follows : 
Albugo. A. Candida is the 
white rust which attacks mem- 
bers of the mustard family, 
causing distortions, especially in 
the flower clusters. The myce- 
lium traverses the intercellular 
spaces of the host, the haustoria 
sent into the host cells being 
slender branches which enlarge 
at the ends into little knobs. 
The sporophores arise in clusters 
and press up the epidermis, which 
then appears like a white blister 
(fig. 158). Finally the epidermis 
is broken and the sporophores are 
, , .. . FIG. 158. Albugo Candida (white rust): 
exposed, each ending in a chain showing mycelium crowd i n g among host cells 
of spores (conidia), which have and sending into them small button-like 
been formed by successive ab- haustoria, sporophores arising under epidermis 
. . . , and abstricting multinucleate conidia (spores), 
Stnctions Of the sporophore. The and the det a c hed and dying epidermis.- 
conidia are multinucleate, and After CHAMBERLAIN. 
