266 



THE FUNGI WHICH CAUSE PLANT DISEASE 



structures are regarded by Hasselbring ^^^ as organs of attachment 

 to aid in infection, though they doubtless serve other pxu-poses as 

 well. 



Perithecia of this species were first obtained by Clinton ^^^ who 

 grew them in abundance on artificial media from sowings of coni- 

 diospores taken from ptire cultures. The typical Gloeosporium 

 stage was also grown from ascospores. 



Perithecia were also found in pure cultures on apple agar by 

 Spaulding and von Schrenk. They appeared in black knotted 

 masses of mycelium which were often 4r-5 mm. in diameter, the 

 perithecia varying from one to many in each such stroma. The 

 asci were evanescent, disappearing soon after the spores matured. 



That this fungus is the cause of a limb canker was suggested by 

 Simpson's discovery of the canker in July, 1902 and was definitely 



proved by Spaulding 

 and von Schrenck,^^* 

 and by Burrill and 

 Blair ^*' in the same 

 year. 



In canker forma- 

 tion the mycehum 

 grows in the live 

 bark, killing it and 

 the cambium. The 

 cankers are thought 

 to be comparatively 

 short lived, perhaps 

 surviving only the 

 third year. Reciprocal inoculations between fruit and twigs 

 have proved the fungus in the two cases to be identical. Conidia 

 and ascospores develop on both fruit and twigs. 



The fungus has been repeatedly grown in pure culture on numer- 

 ous media by many investigators and many inoculations with 

 conidia into both fruit and twigs have proved the causal relation 

 of the fungus to the apple rot and twig canker. Inoculations from 

 ascosporic material have given the same results. 



That the spores may be insect-borne was shown by Clinton; "" 

 that they may also travel on the wind was shown by Burrill,^" 



Fig. 195. — G. rufomaculans, 

 Note septa and appressoria. 

 von Schrenk. 



germinating conidia. 

 After Spaulding and 



