260 



FUNGOUS DISEASES OF PLANTS 



are produced within which areas the pycnidia may be found. 

 Cuttings may also be affected. 



The fungus. The pycnidial stage is a characteristic Phoma or 

 Phyllosticta, ioo to 120/i in diameter, as shown in Fig. 113. 

 These are distributed over the affected surfaces, and produce 

 abundant conidia, which are hyaline, obovoidal, frequently trun- 

 cated at the apex, measuring 10. 5-1 3.5 X 5-6 /*. The conidia are 

 appendaged, and they are expelled from the perithecium much as 

 in the black rot of the grape. The ascogenous form is less com- 

 monly found. In this the perithecia are much as those already 

 described, except that the wall is denser and they bear only asci. 

 The latter are more or less clavate, with a total length of from 



Fig. 113. Guignardia Vaccinii on Cranberry : Pycnidial and Ascigerous 

 Stages. (After Shear) 



60 to 80 /j.. The spores are hyaline when young, and tinted when 

 old. They are described as elliptical or subrhomboidal in form, 

 with granular contents (Fig. 113, b). 



This fungus has been carefully cultivated, cultures being made 

 from both stages and from hyphas, as well as from the tissue of 

 the host beneath the scalded area upon the berries. It is reported 

 to grow well upon acid and neutral media, and especially vigorous 

 upon corn meal in various combinations. The pycnidial form has 

 been produced in culture ; yet in many cultures the conidia are 

 not produced in the perithecia, but the latter remains as a more 

 or less sclerotial organ. The ascogenous form, however, has been 

 secured in cultures from both berries and leaves. After a few 

 generations in culture tubes, the fungus appeared to lose con- 

 siderably in vitality, and frequently developed no spore forms 



