TYPES OF CRYPTOGAMS; THALLOPHYTES 227 
both can be found in one sorus. The spores may be taken from 
the host-plant on the point of a knife by picking rather deeply down 
into the sorus. Place the small quantity of spores so obtained in 4 
drop of water on a slide, spread with dissecting needles, and cover. 
Examine under a power of 200 or 
more diameters. 
The red spores (uredospores) have 
each a stalk from which they easily 
fall. They may be seen attached to 
their stalks if properly prepared 
cross-sections through the sorus are 
available, especially if the material 
is fresh. Examine the spores and 
note the shape, color, and surface. 
If the spores are shrunken, a drop 
of potash solution will restore the 
natural plumpness. Draw. Spore- 
measurements are important in 
determining species. The uredo- 
spores of Puccinia graminis may be 
distinguished from those of other 
species common on grasses by the 
greater proportionate length. 
The structure of the black spores 
(teleutospores) can be made out with- Fic. 162. A Group of Spores of 
out dificulty. Some should be found Wheat Rust (Puccinia gram- 
attached at the base. Note the inis). (x about 440.) 
parts and the differences in color in  y, y, uredospores; ¢, a teleutospore. 
different portions. Make careful 
drawings to show shape and structure of both kinds of spores. 
Boil a portion of a rust-injured plant in potash solution, pick it to 
pieces on a slide under the magnifier or dissecting microscope, use a 
cover-glass, and examine the preparation for mycelium, using a high 
power. 
" 291. Cultivation on a Host-Plant. — If practicable, find some wheat 
or grass which has remained over winter with the black rust upon it. 
Tie a bunch of this to a barberry bush while the leaves are young 
or unexpanded. When the time arrives for the appearance of the 
