380 BOTANICAL GAZETTE june 



of the neck in this genus seems to be quite variable. While Klebahn 

 found that the necks of Gnomonia veneta from sycamore leaves were 

 very short, on sterilized leaves in the laboratory, on which he also 



w 



produced the perithecia, the necks were very long. I have also found 

 in my study of Gnomonia rubi Rehm., a form found on blackberries, 

 that the same variation occurs. The necks in pure culture were twice 

 as long as those growing normally out of doors. Since this is the only 

 difference observed between the forms on sycamore and white oak, 

 it seems best at present to consider them the same. 



The perithecia on the oak leaves also very often push themselves 

 entirely out of the leaf {fig. 6). There is often no leaf tissue below the 

 perithecium, but its beak passes entirely through the leaf and 

 projects on the opposite side. The large perithecia are easily seen 

 on the leaf with a hand lens, when they appear, as black globose 

 bodies apparently lying on the surface {jig. 8). 



The spores are unevenly 2-septate, as in the form on sycamore. 

 In germination, the spore swells considerably and then sends out 

 tubes from any place on the wall of the larger cell {fig. 26) . 



The Sporonema stage was not observed on the white oak, though 

 leaves were examined repeatedly for it; but it developed on oak leaves 

 that had been put in tubes, sterilized, and inoculated with a pure 

 culture from the conidial stage on the leaves. The tubes were kept 

 in a cool place during winter to see if the perithecia would develop. 

 On examination in the spring, no perithecia w^ere found, but there 

 were many pycnidia-Hke pustules, perfectly homologous with those 

 that developed on the sycamore leaves normally. 



The Myxosporium stage was found on the ends of twigs on a few 

 trees about July i, the twigs being killed back in the same manner 

 as the sycamore twigs.' However, on the white oak the young leaves 

 did not start to develop and then die, as on the sycamore; but the 

 twigs w^ere killed before the leaves started. Anthracnoscd spots on 

 the leaves were numerous in close proximity to the diseased twigs, 

 while they were fewer where no diseased twigs were found. It seems 

 very evident from this that the Myxosporium stage is ver>' instru- 

 mental in the early infection of the leaves. The spores in the pustules 

 were not different from those on the leaves, and furthermore, they 

 produced the same colony in agar. 



