Parasitic and Saprophytic Fungi in Orchards. 197 



lower inky black, which is very characteristic of its cultural ap- 

 pearance. The pycnidia were also formed on naturally infected 

 apples brought into the laboratory from the orchard and placed 

 in damp-chambers. 



The strange feature about Sphaeropsis is the fact that at 

 no time did it appear in the trap cultures. Since it has been 

 found to grow so luxuriantly in cultures, it is not because the 

 spores are not viable. The only explanation for its absence is 

 in the peculiar type of pycnidium, which has been found for 

 Sphaeropsis malorum/'' This new form of Sphaeropsis has a 

 closed pycnidium. The spores, too, are larger than the ones 

 described for this species. A careful microscopic examination 

 of spores taken from the pycnidia of some of the twigs showed 

 that the spores were of the same size as those described for this 

 new form. This'would seem to indicate that there is a certain 

 definite time when the pycnidia are open and the spores are 

 capable of producing infections. This period does not occur, 

 apparently, from September to June. 



Paddock, t in his work on the "New York Apple-tree 

 Canker," caused by Sphaeropsis malorum, says that infection 

 usually takes place in the spring in the crevices of the bark. 

 Growth stops in mid-summer and the spores are ripe by August. 

 From this it would seem that the spores should have been ob- 

 tained in the exposures. Since the form with the closed pycnidia 

 is the most common here, the explanation of the absence of viable 

 spores probably lies in this structural character. 



EFFECT OF CLEAN CULTIVATION. 



At first the exposures were from fifteen to twenty minutes 

 duration. This time was limited, subsequently, until from one 

 to two minutes was adopted as a sufficient time. This was 

 found to yield just the same forms as longer exposures. In 

 every case the plates were placed upon the ground. By so 

 doing one might expect that the fungi which appeared would 

 not be representative of existing conditions. Instead of coming 

 from the trees, some might hold that the spores came from the 

 ground cover. This is true only in part. One of the stations 

 was chosen on a strip on which nothing was grown, yet it showed 



♦Walker: Annual Report Nebr. Exp. Station. 21:34-44. 1908. 

 tPaddock: BuUetin N. Y. Agricultural Exp. Station. 163:1-6. 1899. 



