THALLOPHYTES 81 
Among the higher Basidiomycetes the basidia form a definite layer 
(hymenium), whose structure and position are important in classifi- 
cation. As yet, the classification of this great group is very uncertain, 
but for our purpose two great series may be recognized. 
I. Protobasidiomycetes, in which the basidium is four-celled, each cell 
bearing a spore; and II. Autobasidiomycetes, in which the basidium 
is one-celled and bears four spores (or at least produces four nuclei). 
I. PROTOBASIDIOMYCETES 
(a) Ustilaginales 
General character. These are the smuts or brand fungi, destructive 
parasites that attack the floral and other organs, notably the ovaries 
of grasses, and are of course best known in connection with their 
ravages among cereals. Ustilago Maydis, the corn smut, may be taken 
as a representative. 
Corn smut. The mycelium may infect any part of the host, even 
the roots, and may give external indications of its presence in any re- 
gion. At the time of flowering, for example, the ovary may become 
packed with mycelium, which causes a distorted, swollen, tumor-like 
growth. These tumor-like swellings may be observed also in other 
parts of the plant, including the tassels. Later this mycelium forms 
additional cross walls; the short cells become rounded off and thick- 
walled, and the mycelium is thus transformed into a mass of black 
spores, which are the so-called brand spores, the whole mass being the 
so-called smut. This kind of heavy-walled spore, which is a trans- 
formed vegetative cell of a septate mycelium, is called a chlamydospore, 
the name referring to the heavy, protective wall. These spores fall to 
the ground and pass the winter. Upon germination in the spring, the 
spore develops a short filament of three or four cells. This filament is 
saprophytic and each cell buds out spores laterally and the end cell ter- 
minally, suggesting conidium-formation. If abundant food supply is 
available, spores continue to be abstricted in great numbers ; and may 
be multiplied further by the yeastlike budding of the spores (see p. 70). 
This filament of three or four cells is thought to represent the basidium, 
but in this case the very indefinite number of spores produced obscures 
the resemblance. The spores produced, therefore, are probably basidi- 
ospores, and the brand spores hold the same place in the life history 
of smuts as that held by the teleutospores in the life history of rusts 
C. B. & C. BOTANY 6 
