gi 
found that the pustule is formed by the rupture of the 
epidermis of the leaf. Large numbers of the orange 
uredospores arise under the skin and burst through to the 
outside. The torn edges of the epidermis thus act as a 
boundary to the pustule. The filaments of the fungus 
ramify in the tissues of the leaf often sending special 
branches called haustoria into the living cells from which 
nutriment is thus absorbed. The reproductive branches 
of the fungus grow outwards and accumulate in rows 
under the skin of the leaf. The round, orange uredo- 
spores are produced on the tips of such branches, and 
are liberated when the epidermis bursts under the pres- 
sure. Each uredospore is a single, oval cell about a 
thousandth of an inch in length, and readily falls 
free from the stalk bearing it. The wall of the spore is 
studded with minute warts and has four thin round pores 
near the middle part. The uredospores are able to ger- 
minate, immediately they are liberated, in a film of water 
or in damp air. Through the pores mentioned above two 
or three fine filaments grow out; one of these usually out- 
strips the rest and may become a long, branched, wavy 
filament. If in water alone, or indeed apart from a living 
leaf of the wheat plant, this filament is only able to survive 
until the small store of reserve food material in the spore 
is exhausted. If, however, the spore germinates on the 
leaf of a wheat plant the germ tube grows to one of the 
stomata, and passing through the pore enters the tissues 
of the leaf. Here the fungus absorbing food material 
grows and produces a new pustule with uredospores in 
about a fortnight. In this way very large numbers of 
uredospores are produced during the summer months and 
hence the disease spreads rapidly. 
The teleutospores, like the uredospores, arise from 
branches of the filaments of the fungus in the leaf and 
they appear towards the end of summer in the same 
pustules as the uredospores. With the advance of the 
season, however, the pustules give rise to teleutospores 
only. Microscopically, these are longer than the uredo- 
spores, are more spindle-shaped, but are also borne on 
stalks. Each spore consists of two cells and is furnished 
with a thick, resistant wall. Unlike the uredospores the 
teleutospores do not germinate immediately when placed 
under moist conditions, but they require to rest for a period 
of months. If, however, teleutospores which are produced 
