JOlNEOPAGiaaiLTmLlSEARCH 



Vol. XV Washington, D. C, December 23, 1918 No. 12 



PARASITISM, MORPHOLOGY, AND CYTOLOGY OF 

 CRONARTIUM RIBICOLA 



By Reginald H. Colley 



Assistant Pathologist, Investigations in Forest Pathology, United States Department of tift*^ '^^f 



Agriculture g^ *'**^A 



INTRODUCTION ^^dfn^^ 



During the last few years Cronartium rihicola Fischer has become the 

 most serious fungus pest of white pine (Pinus strobus L.) in America. 

 As such it has been the subject of much study by pathologists who real- 

 ized, from a knowledge of the course of the parasite in Europe, the 

 damage it was capable of causing. Spaulding (54)^ in the most com- 

 prehensive paper on the fungus which has appeared in this country, 

 reviews the reports of its ravages on white pine in the Old World and 

 gives its general characters and life history. Since the discovery by 

 Stewart (^7) of C. rihicola on species of Ribes at Geneva, N. Y., in 

 1906, many papers have appeared calling attention to the absolute neces- 

 sity of controlling the spread of this parasite if the white pine is to be 

 saved for reforestation. A great deal of attention has been given to 

 testing the susceptibility of possible hosts through inoculation and to 

 control and eradication methods, both in the United States and Canada. 

 In Europe most of the recent work has been along this same line. Kle- 

 bahn {23, 24, 25, 26) and Tubeuf {58, 59, 60) have carried on extensive 

 experiments. 



The morphology of Cronartium rihicola and the details of the interrela- 

 tions of the parasite and its hosts have never been thoroughly worked 

 out. The cytology of the genus Cronartium has up to the present time 

 received very little attention. In the following paper the results of 

 certain observations extending over a period of two years will be pre- 

 sented, first, with reference to the minute histology of the fungus and 

 the interrelations of host and parasite, and second, with reference to 

 the cytological phenomena accompanying spore production in the 

 different types of sori. The paper is offered as a contribution to our 

 knowledge of the parasitism, morphology, and cytology of the genus 

 Cronartium. 



' Reference is made by number (italic) to " Literature cited," p. 653-659. 



Journal of Agricultural Research, Vol. XV, No. 12 



Washington, D. C. Dec. 23, 1918 



qr Key No. G-169 



(619) 



