162 



In Timothy, timothy-rust (Puccinia Phlei-pratensis Erikss. and Henn- 

 ing) is regarded as the most serious pest. While the different cultures which 

 the writer examined at Svalof, clearly exhibited different attitudes toward 

 this disease, the differences were not so striking as in the case of Orchard 

 grass. 



From the above discussion of the variability of grasses it follows that 

 one of the first steps in practical breeding work is to test the constancy of 

 those mother plants which are isolated for special investigation. This can 

 obviously be done only by providing adequate protection against cross- 

 fertilization and sowing the seeds in separate culture for a sufficient number 

 of generations. 



In conducting this test it is desirable to procure as much seed as possible 

 from the plant under investigation since the larger the culture sown, the 

 smaller will be the experimental error and consequently the more reliable 

 will be the result. In grasses it is an exceedingly simple matter to augment 

 the vegetative system by dividing the roots. Each tiny division becomes a 

 small plant which ultimately may produce practically as large a growth as 

 that of the original mother. 



The system of numbering mother plants as well as their progeny is some- 

 what different in the case of grasses than in that of cereal grains owing to the 

 fact that grasses cross-fertilize readily in nature and thus render it necessary 

 to handle an unusually large number of individuals. All mother plants of a 

 given kind of grass are therefore numbered consecutively, each plant retaining 

 its original number in succeeding generations whether propagated vegeta- 

 tively or not. 



Some idea of the method of grass breeding will be conveyed by an 

 examination of the following diagram : 



