A DISEASE OF PINES CAUSED BY CRONAETIUM PYRIFORME. 13 



along the column with its growth. .The period of teliospore formation 

 for each telium is from one to two weeks. The teliospores germinate 

 in situ as fast as they mature, without being detached from the telial 

 columns. As each teliospore germinates it develops a basidium, 

 which when typical bears four sporidia. The sporidia borne on each 

 basidium, however, are usually less than four. The sporidia become 

 detached as soon as mature and are carried away by even the slightest 

 breeze. They readily infect the younger part of pine trees, thus 

 completing the life cycle of the fungus. From observation it appears 

 probable that germinating sporidia usually gain entrance into the 

 tissues of the pines through wounds or in wound callus where young 

 cells are exposed. Inoculations with another species, Cronartium 

 cerebrum, on pine trees (Pinus virginiana) without wounds have failed, 

 while at the same time, other conditions being similar, they were 

 successful in wounds. 



Since each generation of uredinia on Comandra plants is followed 

 within a few days by one of the telia, there is a continual produc- 

 tion of sporidia from the time the telia first appear till the end 

 of the growing season. This greatly extends the period of pos- 

 sible infection for pines, a period which must be from two to four 

 months, depending upon the length of the growing season in pines, 

 which varies not only at different altitudes and in different latitudes, 

 but also from season to season. 



It is highly probable that the various spore forms of this fungus, 

 especially the seciospores from the pines, may be carried about on 

 the bodies of birds and of the smaller animals. In this manner they 

 could be carried even to greater distances than is possible by wind 

 dissemination. 



If young pines in nurseries should become infected, the danger 

 of a much wider dissemination of the fungus than has already taken 

 place in nature is at once possible, with man as the agent. Under 

 conditions such as occur in many localities both in the eastern and the 

 western United States it would be easily possible for the pines in 

 nurseries to become badly infected, owing to the abundance of Coman- 

 dra plants in the vicinity. 



EFFECT OF THE FUNGUS ON ITS HOST PLANTS. 



EFFECT OF THE ^ECIAL FORM ON PINES. 



The immediate effect of the aecial form, Peridermium pyriforme, 

 varies in different species of pines and on the same species under 

 different conditions. When young lodgepole pines or western yellow 

 pines are attacked, either on the trunk or limbs, there commonly 

 develops a slightly swollen area in the region of the infection. If 

 the infected area encircles the trunk, as it usually does, a spindle- 

 shaped or fusiform swelling may result (PL II, fig. 3), which varies 



