(4") 



putting it in place. If the leaves of the trial host will not moisten 

 they are rubbed between the fingers until the moisture will adhere. 

 The plant is then covered with a bell-jar and set in a shaded place 

 for a period of two or three days. The bell-jars are temporarily 

 removed each day, aired and sprayed on the inside before being 

 replaced. The bell-jar prevents rapid evaporation, thereby in- 

 suring the necessary moisture during the germination and infection 

 period. During this period the plants are screened from the direct 

 rays of the sun to prevent the temperature from rising too high. 

 This scheme of first applying moisture to telia at the time when the 

 sowing is to be made and of suspending the whole twig or gall 

 directly over the parts to be infected has been found vastly better 

 than that of removing the telia or spores, placing them in water 

 and allowing them to germinate, and then attempting to apply 

 the basidiospores with a brush or otherwise, as was first attempted 

 by the writer following the lead of the earlier workers. One ob- 

 jection to the method as outlined above is that in the case of vig- 

 orous germination infection on a very susceptible host may be 

 so great that the host may be severely injured by it and its further 

 development checked. This may sometimes be overcome by 

 washing off some of the basidiospores which can often be observed 

 on the leaves of the trial host as a yellow powder. It is not neces- 

 sary to make special tests for the germination of the spores, as is 

 usually done with other genera of the rusts, for germination can 

 nearly always be detected by the yellow and pulverulent condition 

 of the surface of the spore-masses, if the aggregations of basidio- 

 spores cannot be seen by the naked eye on the trial host leaves 

 as indicated above. In case of doubt a microscopic examination 

 of some spores removed from a telium would soon settle the ques- 

 tion. The species of Gymnosporangium are usually easy to bring 

 to germination and yet some species have given considerable 

 trouble and one species refused to germinate at all although the 

 material was fresh and seemed in good condition. 



Collection and Care of Culture Material 

 Telial material to be used for cultures is best when not collected 

 until mature, and then used for sowing as soon afterward as pos- 

 sible. If fairly large specimens of the branches or twigs with some 

 green leaves are secured, the telia will keep fresh for some time 

 provided they are not allowed to become expanded with moisture. 



