256 INTRODUCTION TO BOTANY 
a period of dormancy, usually lasting through the winter, 
these spores germinate. From each cell of the winter spores 
in the spring there grows a small hypha (fig. 198, #). Each 
cell of this hypha forms one thin-walled spore (sporidiwm). 
This rust (Puccinia graminis) has another stage in its life 
cycle. The sporidia, when alighting upon leaves of a shrubby 
plant known as the barberry, grows and produces within the 
leaf an extensive growth of mycelium. When this mycelium 
produces spores, they appear in a peculiar cup on the under- 
side of the barberry leaf (fig. 198, #). These spores, being 
different from any of the three described, and being formed 
in a cup, are called cup spores. Cup spores reproduce the rust 
plant upon wheat and oats. Summer spores persist through 
the winter, and it is thought that they also reproduce the rust 
upon oats and wheat in the following spring. No satisfactory 
preventive for this fungus has been discovered. Some progress 
has been made by learning which varieties of wheat and oats 
are most resistant to attacks by the parasite.! 
243. Mushrooms. In this sub-division of stalk fungi those 
members that are good to eat have been popularly called 
mushrooms, while those not edible were called toadstools. 
Scientifically there is no accepted distinction of any kind, and 
the name mushroom is now being used for the whole group. 
In a given genus some species may be edible, others not. 
Also, some species are edible while young, but not so when 
older. Some of the more common edible species are easily 
learned and not readily confused with poisonous forms. In 
the United States over one thousand edible forms are known, 
but some of them are very rare. 
244. The general character of mushrooms. The mycelium 
of mushrooms lives entirely within the material which fur- 
nishes its nourishment, and from this mycelium it may send 
up into the air the spore-bearing structure commonly regarded 
as the entire mushroom. The mycelium becomes very exten- 
sive and forms moldy or cobweb-like threads within the rich 
1 Rusts of Cereals,’? Bulletin 109, 8.Dak. Agr. Exp. Sta., 1908. 
