320 



PLANT DISEASES 



Numerous minute sclerotia are formed in the dying 

 leaves ; these remain in a passive condition until the 





n 

 / 



I V 





/:/ 



Fig. 87. — Heterosporium echinulatum. i, portion of a 

 diseased carnation ; 2, a small tuft of fungus fruit, showing 

 the large, minutely warted, septate spores borne singly at the 

 tips of crooked sporophores ; a, portion of a compact mass 

 of mycelium from which the cluster of conidiophores spring, 

 and which eventually forms a sclerotium, x 300; 3, a spore 

 that has germinated in water ; the germ-tubes bear short 

 branchlets, each of which produces a dark-coloured secondary 

 spore at its tip, x 300. 



following season, when they produce minute conidia, 

 which, when placed on living leaves of carnation, give 

 origin to the first patches of disease. 



