91 



found that the pustule is formed by the rupture of the 

 epidermis of the leaf. Large mimbers of the orange 

 uredospores arise under the skm 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 w^arts and has four thin round pores 

 near the middle part. The uredospores are able to ger- 

 minate, immediately they are liberated, m 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 becomie a long, branched, wa^ y 

 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 growls 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 wath uredospores in 

 about a fortnight. In this w^ay 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, how^ever, 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 

 tinder moist conditions, but they require to rest for a period 

 of months. If, however, teleutospores which are produced 



