THE FUNGI WHICH CAUSE PLANT DISEASE 



81 



germinate in a similar manner. Conidia germinate freely only if 

 they are chilled. ^^ 



A. Candida (Pers.) Roussel.*' Sori on all parts of the host except 

 the roots, white or rarely light-yellow, prominent and rather deep- 

 seated, variable in size and shape, often confluent and frequently 

 producing marked distortion of the host; conidiophores hyaline, 

 clavate, about 35-40 x 15-17 m; conidia, globular, hyaline, with 

 uniformly thin walls, 15-18 fi; oospores, much less common than 

 conidia, usually confined to stems and fruits, chocolate-colored, 



Fig. 53. — A. bliti, young oogo- 

 nium and antheridium show- 

 ing nuclei. After Stevens. 



Fig. 54.— a. bliti, 

 showing differ- 

 entiation of 

 ooplasm and 

 periplasm, the 

 nuclei in mito- 

 sis. After 

 Stevens. 



Fig. 55. — A. bliti, an- 

 theridium showing 

 the multinucleate 

 tube. After Ste- 



40-55 p.; epispore thick, verrucose, or with low blunt ridges 

 which are often confluent and irregularly branched. 



This is the most widely distributed and most common species 

 of the genus. It occurs throughout the world on a large number 

 of cruciferous hosts, and often gives rise to very pronounced 

 hypertrophy. Practically all cultivated crucifers, cabbage, 

 radish, turnip, etc., are subject to attacks of this fungus. In 

 Europe the caper and mignonette are attacked by the same 

 species. It has been reported in New York on Tropceolum.^* 



A. ipomoeae-panduranse (Schw.) Sw.^^' "" Sori amphigenous or 

 caulicolous, white or light yellow, prominent, superficial, 0.5- 

 20 nmi., rounded, often confluent and frequently producing 

 marked distortions of the host; conidiophores hyaline, clavate. 



