UREDOSPOKES 



!» 



The Uredospores. 



The germ-tube soon forms a more or less extensive m\ 

 celium, which may penetrate the greater pari of the leaf of 

 the Garex, but in many species of Puccinia is strictly localised 

 to a small defined spot. All its cells are binucleate, like the 

 spore from which it originated. The cells of the mycelium, in 

 every stage, send haustoria into the cells of the host : when an 

 haustorium arises from a binucleate mycelium, it is itself 



Fig. 8. Section of leaf of Garex. paludosa, with a sorus of uredospores of 

 P. Caricis ; a, upper epidermis ; 6, a vascular bundle. Most of the 

 pedicels have lost their spores. x 180. 



likewise binucleate. After a few days this mycelium begins to 

 form the third kind of spore — the uredospore. A knot of 

 hyphse is formed just beneath the epidermis ; some of the 

 branches turn upwards and form a regular 

 layer parallel to the surface — the spore- 

 bed (Fig. 8). 



The upper rounded cell of each hypha 

 is divided into two daughter-cells, the 

 lower of which is developed into a 

 stalk, the upper becomes the uredospore 

 (Fig. 9). The spore is oval or roundish : 

 when mature it is enclosed in a double 

 cell- wall, the outside being cutinised and 

 provided with spine-like projections, some- 

 what like those of the secidiospore, only 

 more pointed. In the inner layers of the 

 exospore there are usually three (rarely 



Fig. 9. P. Caricis. De- 

 veloping uredospores 

 (1, 2, 3, 4, show stages 

 of growth ; 5 is a pe- 

 dicel from which the 

 spore lias vanished), 

 x 500. 



