3 66 



FUNGOUS DISEASES OF PLANTS 



disease is distinguished from the leaf spot by smaller spots more 

 colored when young and more nearly circular. They are also 



less clearly defined on the under 

 surfaces. 



The blight also attacks the fruit. 

 In this case the spots are at first 

 red but later darker in color. The 

 drying of the surface layers accom- 

 panying the effects of this disease 

 may cause a cracking very much 

 as in the case of pear scab. 



The fungus. The larger spots 

 of the leaf blight will generally 

 show at the time of leaf fall one 

 dark papilla in the center of each. 

 This papilla is an indication of 

 an acervulus, or spore-producing 

 stroma. The mycelium from which 

 this stroma originates penetrates 

 the epidermal layer and also to 

 some extent the hypodermal tis- 

 sues, and the affected region shows a general collapse of the 

 cells. From the subcuticular stroma there are produced on minute 

 conidiophores numerous "insect-like" spores (Figs. 185, 186). The 

 spores germinate readily and the fungus is thereby spread during 

 the same season. 

 Various authors 

 have described what 

 is supposed to be a 

 perfect stage of this 

 fungus. Sorauer 1 



FIG. 185. ENTOMOSPORIUM MACULATUM 



has referred the 



ascogenous stage to Stigmatea Mespili. Atkinson 2 has found this 

 fungus on wintered leaves of the quince and has considered it to 

 be a member of the genus Fabraea. 



Control. Experiments upon nursery stock have shown that 

 Bordeaux mixture of any standard strength may be used success- 



1 Pflanzenkrankheiten, I.e. (cf. p. 371). 2 Garden and Forest 10 : 73-74. 1897. 



FIG. 184. ENTOMOSPORIUM ON 



QUINCE. (Photograph by H. H. 



. Whetzel) 



