1913.] PUBLIC DOCUMENT — No. 31. 43 



sjiores. On the surface of these so-called strings are deposited 

 tinj cells known as sporidia. These sporidia will germinate 

 only on the bark of young shoots of the white pine. 



The so-called sporidia are produced and carried about by the 

 wind at the very season when the young pine shoots have begun 

 to develop and are in a condition to be readily infected. When 

 the small sporidia germinate they send their germ tubes into the 

 tender bark of the white pine, and there the mycelium again 

 forms a heavy matting. This tissue lives for many years in the 

 branches, and occasions considerable swelling of the shoots, by 

 which the disease may be detected in the fall and winter, when 

 there are no yellow deposits on the bark. These swellings often 

 do not show on the white pine for perhaps a year or more. It 

 is probably several years after infection before these dark yellow 

 spore blisters are formed, but when they once appear they often 

 reappear every spring for a number of years on the same swell- 

 iugs. Their appearance is preceded by the formation of very 

 small dot-like heaps of spores which are called spermogonia. 

 These spermogonia contain sweet-tasting, sticky spores, so-called 

 spermatia, about which nothing is known. 



It will be seen from the preceding that this disease cannot 

 spread from one pine to another. It must first go from pine to 

 Eibes (in May or June) and from Ribes back to pine (in Au- 

 gust or September). In the trunks of pine trees the fungus is 

 perennial, but on Ribes it affects only the leaves and cannot 

 live over winter. 



While it would appear from this description of the rust that 

 an alternation of hosts is necessary in the case of currant rust, 

 some American pathologists would question this, and observa- 

 tions made by some investigators on the rust in this country 

 seem to indicate that the rust may be able to propagate iudefi- 

 nitely on the currant without the intervention of the pine. 



At the request of Professor Stewart we are therefore conduct- 

 ing experiments to determine whether reinfection of currants 

 can occur without the intervention of the pine. These are now 

 being carried on in our greenhouse, together with some other 

 experiments relating to the control of the disease; and work 

 along the same lines is being done by Dr. Clinton in Con- 

 necticut. 



