and Laboratory Methods. '2118 



and apply it at many scattering points over the leaves of each of the healthy 

 plants. These plants should first have been well sprinkled with a good atom- 

 izer which produces a very fine spray, thus covering the leaves with very 

 minute drops of water. The rust spores are thus scattered about in these 

 little drops of water. After the inoculations the plants should be again 

 sprayed with the atomizer and then covered with a bell-jar and kept covered 

 for an average of two days' time, after which the bell-jar may be taken off 

 and the plants may remain exposed until the experiment is finished. In the 

 summer season it is best to make the inoculations in the evening. If there 

 is much direct sunshine, the bell-jars should be kept covered with newspapers 

 during the time the sun is shining. In all inoculation work, extremes of 

 temperature and intense sunlight must be avoided. The period of incubation, 

 that is the time from the inoculation until the new rust sori appear, varies 

 considerably for different species, and in the same species will occasion- 

 ally vary some for different hosts. For the uredo stage of the common leaf 

 rust of wheat {Piicdnia rubigo-verd) it averages about nine days. For the 

 uredo stage of corn rust this period is considerably shorter, being, in some 

 cases known to the writer, only five days. In other cases the period of 

 incubation is sometimes fifteen to twenty days. This period is always much 

 longer where teleutospores are used to produce aecidia. In such cases the 

 spermagonia appear first after a week or ten days, the aecidia following a 

 week or more later. 



Suggestive Studies. I have already mentioned the use of the uredospores in 

 inoculation work with grains and grasses, as being material that is easily handled. 

 In cases of heteroecious rusts, the secidiospores can be just as readily used for 

 producing other stages on the host to which they belong. For example, if bar- 

 berry rust happens to exist in sufficient quantity to be readily obtained, material 

 of this rust can just as easily be used to produce other stages of /-*. gramiiiis 

 on wheat and oats as to use the ordinary uredospores. The reverse operation 

 of using the teleutospores of wheat and oat rust to infect the barberry requires a 

 little more patience at first, but can also be readily performed after one becomes 

 a little more skillful in this kind of work. A good species also for the work of 

 beginners is, of course, the common cedar apple which produces the apple leaf 

 rust. In April, after a period of rains, this rust of the cedar germinates so 

 easily that the operation can often be carried out very simply and quickly in watch- 

 glass cultures. The germinating material can then be readily sprayed on the 

 leaves of the apple seedling by means of an atomizer. It seems usually better, 

 however, to simply spray the leaves with water, as already mentioned, and apply 

 the germinating spores independently. 



It is with the enormous number of rust forms infesting the grasses that the 

 investigator has the largest field for original work in this line. All the knowl- 

 edge possible to us from a morphological standpoint alone only leaves these forms 

 in the utmost confusion, and it will require diligent work of a number of special- 

 ists for years to place them where they belong. 



Inoculation experiments are not only intensely interesting, but are certainly 

 the very best means to be used by the teacher in demonstrating some of the 



