2112 Journal of Applied Microscopy 



material should be left outdoors during the winter in order that it may undergo 

 all the ordinary chanj,es of weather that occur in nature. 



During the latter part of March or in April, germinations are usually readily 

 obtained with most species. It will be found that germinations will be especially 

 easy if the material has passed through extreme changes of warm, wet weather 

 and freezing temperatures accompanied with snow, such changes following each 

 other rapidly. It is by this means that the writer was finally able to germinate 

 the peculiar amphispores in the species P. vexans. 



Methods of Inoculation. Under the head of Germination Studies I might have 

 mentioned that where it is difficult to keep material fresh on account of having 

 to get it from a distance, the best method is to collect the plants entire, including 

 roots, and keep them in an ordinary tin collecting can. If one wishes to use the 

 material for a week or two weeks, if possible the plants should be taken 

 up by the roots and planted in pots in the greenhouse. By following 

 this method one can soon have quite a collection of plants in the 

 greenhouse with the rust forms from which material may quickly be 

 obtained for carrying out inoculation experiments. In making inocula- 

 tions, either germinating spores in water cultures may be used, or 

 the material may be taken directly from the infected plant and applied to the 

 healthy plants on which one wishes to make the infection. Because of the 

 additional labor required in making a water culture, it is more convenient to make 

 the infections directly from the infected plant. There will be occasionally 

 instances, however, where, negative results being obtained, one wishes to know 

 whether the spores are really in condition for germination, and, therefore, 

 needs first to make water cultures in order to answer that question. One of 

 the principal objects, of course, in inoculation work is to determine to what hosts 

 the particular rust under study belongs. Aside from this, however, there are 

 many interesting things to the student concerning the manner of the growth of 

 the rust, the period of incubation, etc., which may be learned through these 

 studies. Inoculations for the particular purpose of determining the hosts of a 

 rust are most readily made with uredospores. It is evidently a further confirm- 

 ation of one's conclusion, however, in the case of hetercecious species if one 

 employs also the other spore forms. Of course, in all inoculations, the 

 new host must be grown from the seed, or one cannot be sure that the 

 rust is not already present. 



As most of my own work has been with the grains and grasses, I 

 shall give illustrations from that group of plants. The seed is planted 

 ordinarily in three-inch pots and kept in those pots until the experiments 

 are entirely completed. The inoculations are best made when the plants 

 are from three to five inches above the surface. The manner of making the 

 inoculations is as follows : 



Five to a dozen pots, containing each a different host to be inoculated by 

 the same rust, are grouped together on a bench having a bottom of sand, 

 at some point in the greenhouse where there are no great extremes of tem- 

 perature. Then by means of a thin bladed scalpel, scrape a little material 

 from some of the spots of the infected plants, where it is most abundant. 



