abstracts: mycology 377 



occurs naturally in South China, very much isolated from sources of 

 citrus-canker infection. The abundance of cankers found on such 

 trees gives rise to the theory that this species may have been an original 

 wild host from which citrus-canker spread to cultivated species. 



H. R. Fulton. 



MYCOLOGY. — The parasitism, morphology, and cytology of Cronar- 

 tium ribicola Fischer. Reginald H. CollEy. Journ. Agr. 

 Res. 15: 619-659. Pis. 48-53. December 23, 1918. 



In the white pine the myceUum of the fungus makes its way between 

 the cells of the phloem tissue, passes into the xylem along the rays, 

 and in some instances works its way between tracheids. The severe 

 damage to the tree attacked results from the driving out of the bark 

 after formation of the aecia and a consequent girdling action. Before 

 spore formation, the pine cells are quite tolerant of the presence of the 

 hyphae of the parasite. The mycelium in Ribes leaves is scattered; 

 haustoria are much less prominent and abundant than on the mycelium 

 in the pine host. The damage to Ribes varies greatly according to the 

 susceptibility of the species. 



Pycnia are formed in broad layers just under the outer cork layers of 

 the bark. The aecia, more deeply seated than the pycnia, are formed 

 on the same general area as the pycnia, following the latter by one 

 season. The aecial peridium is three to five cells thick. Uredinia are 

 formed on the lower surface of the infected Ribes leaves, and are at 

 first covered by a peridium one cell in thickness. The teliospores are 

 produced in columns which in their young stages are identical with the 

 young stages of the uredinia, having the same type of peridium. Every 

 teliospore in the column may germinate. 



The cytological processes agree very closely with those observed by 

 previous investigators on other rusts. At the inception of the dikaryon 

 at the base of the aecium, the union of two fertile cells regularly occurs, 

 but a number of cases were observed where several cells formed a large 

 placenta-like unit from which the aeciospore chains appeared to arise. 

 The similarity of the processes of conjugate division in the dikaryon 

 in the aecia, m-edinia, and telia, suggests a stability of nuclear material 

 throughout the dikaryon. The presence of centrosomes in the nuclei, 

 and occurrence of a number of chromesomes in excess of two, is dis- 

 cussed and illustrated very fully. R. H. C. 



