129 



microscope under the ordinary liigh power. Melampsoraceous species 

 are best tested in a moist cliamber, sucli as a Petri dish, without being 

 removed from the host. Growth can be detected by the unaided eye, or 

 with a hand lens, by means of the light yellow sporidia which cover the 

 sori, making them appear pulverulent instead of waxy. Teliospores of such 

 species as the Coleosporiums germinate as soon as mature, which is in 

 the fall of the year. They are sown when fresh and if suspended over a 

 slide in a moist chamber, the sporidia drop upon it, and their germination 

 can in turn be observed with the aid of the microscope. 



For indoor experiments, small but vigorous growing potted plants are 

 used as trial hosts. Since the pots must be handled, it is desirable to 

 select plants with as small roots as possible and still have them maintain 

 their vigor. The tops are placed under bell-jars when the spores are 

 sown, and in order to have them cover more readily all extra foliage is 

 carefully pruned away. A few young and vigorous leaves are all that is 

 required. 



The manner of applying the spores to the plants differs slightly ac- 

 cording to the kind of spores. If they are aeciospores the leaves bearing 

 the aecia are suspended over the portions to be infected, in such a manner 

 that as the spores fall from the cups they will light upon the desired 

 area. In all cases the host plant is first sprayed, the parts which will not 

 wet being rubbed with the fingers until water will adhere. The spores do 

 not need to be placed in water, in fact they should not be. Teliospores 

 readily begin the germination process in water but seldom form their 

 sporidia there. A moist surface and a saturated atmosphere are necessary 

 factors for the germination of all kinds of spores. Urediniospores and 

 teliospores are removed with a knife or scalpel blade, care being taken 

 to apply the edge to the sorus in such a manner as to loosen the spore 

 by breaking the pedicle, leaving the cell-wall uninjured. If certain areas 

 to which the spores are applied be marked by pieces of thread the watch, 

 which must be maintained for the first sign of infection, will be greatly 

 facilitated. 



To secure reliable results, it must be positively made out that a 

 plant is free fi*om infection when a sowing is made. Wild or native 

 plants brought in from the field or garden should remain in the green- 

 house a period of eight or ten days so as to preclude a possibility of out- 

 side infection. 



9— A. OP Science. 



