THE BLIGHTS 



245 



the host. The type most available for study is the blister 

 blight (Albugo), but the potato blight, or rot, 

 and the grapevine blight (downy mildew) are, 

 for economic reasons, the most important forms 

 in the group. 



Tlie Uister blight. The blister blight (Albugo) 

 grows on the shepherd's purse (Capsella) and 

 not Infrequently on the radish, appearing as 

 white blisters on the leaves and stems (Fig. 215). 

 The blisters are formed by the asexual fructifica- 

 tions, which consist of masses of spores called 

 conidia that are developed in chains from the (Albugo Candida) 

 ends of hyphse just underneath the epidermis Blisters containing 

 (Fig. 216, A, B}. Conidia are air spores of fungi, conidia on the 



, , , . P i -i . , . stem of the shep- 



that is, spores formed singly or in chains at herd's purse 



the ends of special branches and scattered in (Capsella) 

 the air. Those of Albugo are distributed by the wind after the 

 breaking of the blisters, and germinate in moisture, developing 



FIG. 215 

 The blister blight 



FIG. 216. Reproductive organs of the blister blight (Albugo Candida) 



A, section through the edge of a blister on a leaf ; the air spores, or conidia, are 

 formed in chains under the epidermis from the swollen tips of fungal filaments 

 growing between the cells of the leaf; B, tips of two filaments, showing devel- 

 opment of the conidia serially ; C, a filament showing sucker-like structures 

 (haustoria) which enter the cells of the host ; D, the sexual organs ; the male 

 cell, or antheridium, a, has just discharged its nucleus through a beak-like 

 process into the single egg within the oogonium 



