28 



The ^cidiospores are formed from the latter part of April up 

 to as late as July ; the appearance of a plant infected by them is 

 described by Fig. i, PI. II. When the spores fall upon the leaf 

 of a corn or grass plant they germinate in from seven to ten 

 days if moisture is present. The filaments of the germinating 

 spores enter the stomata, and form the mycelium developed in 

 the tissues of the leaves. Uredospores are formed in longitu- 

 dinal red blotches, or sori, upon the leaves and stems of the 

 host plant, as shown by Fig. 2, PI. II., and in this stage the fungus 

 is usually denominated Uredo linearis. One of these pustules 

 considerably magnified is given in Fig. 3, PL II. A vertical 

 section of a sorus, more highly magnified (Fig. 4, PI. II.), 

 shows under the broken upturned epidermis of the leaf the 

 branching hyphae with spores. These spores are soon disen- 

 gaged and disseminated by the wind, or other agencies, and ger- 

 minate in favourable circumstances in a few hours upon wheat, 

 oats, rye, and some grasses. Their shape and appearance are 

 indicated by Fig. 5, PI. II., very highly magnified, and on either 

 side of the spores are shown germ tubes put forth from them in 

 the process of germination. There may be several generations 

 of this uredo form of the fungus during the season. 



After a time a change occurs in the colour of the spores that 

 are produced. The spores become dark brown, and finally 

 black. The sori also turn to black brown, and the spores 

 then are termed teleutospores, or the final spores. This 

 change happens as the host plants ripen, and is caused by the: 

 process of maturing. And it is at this stage that the fungus 

 does the most mischief, or it may even be said its chief 

 mischief, as the host plants require all their starch for forming 

 seed at this period.* If there is much moisture at this time 

 favouring the development of the fungus, it frequently happens 

 that the straw is thickly covered with the black pustules, and 

 the grains of corn are shrivelled because of the abstraction of 

 the starch necessary to make them perfect. As a rule, the first 

 stage, or the uredo stage, with its reddish yellow spores, is not 

 particularly harmful to corn plants, unless the season is excep- 

 tionally favourable for its development. 



The peculiarly shaped black pustules, or sori, of the teleuto- 

 spore stage, on the straw of corn plants, are delineated in Figs, 

 6 (natural size) and slightly magnified at 7, PI. II., and are shown 

 considerably magnified in Fig 8, PI. II. If a section of infected 

 straw is examined it is found that the tissues of the cells have 

 been completely broken down by the action of the mycelium of 

 the fungus, and the teleutospores can be seen upon their hyphae 

 (Fig. 9, PI. II.). These teleutospores are quite different in shape 

 from the uredo spores, being shaped like a club, and dark brown 

 or blackish, in colour, f They are divided in the middle by a wall 

 or partition, so that they form two cells. (Fig. 10, PI. II.) 



As is well known, parasitic fungi cannot form starch like other plants 

 which have chlorophyll, and must get this food from the host plants. 



f Uredo spores and teleuto spores can sometimes be found together 

 coming from the same mycelium, or centre. 



