IOO MAINE AGRICULTURAL, EXPERIMENT STATION. I916. 



that cross-pollination does not occur is that the anthers shed 

 their pollen before the glumes open, and there is very little 

 chance for the introduction of foreign pollen. Consequently 

 we may assume that for many generations the ancestors of any 

 particular oat plant growing in a field or plot have been self- 

 fertilized and that this plant will breed true to its hereditary 

 characters. This is the fundamental assumption upon which all 

 pure line breeding is based. By the selection and isolation of 

 such pure lines out of ordinary commercial varieties new strains 

 may often be secured which are far superior to the parent vari- 

 ety. 



The point in question can perhaps be made still clearer by con- 

 sidering what constitutes a commercial variety. To the casual 

 observer a variety may appear to be breeding perfectly true and 

 all the plants may appear to be alike. However, if the plants 

 are examined carefully many differences will be found. Some 

 have larger heads, or more spikelets per head, others have a 

 larger number of culms, some have stirrer straw than others, 

 etc. Some of these differences are due to environment, such as 

 more space or better ground. On the other hand some of these 

 variations are definitely inherited. If individual plants are 

 selected and the seed of each grown in separate rows, it will 

 be found that many of these rows differ greatly in their yield, 

 time of maturity, strength of straw, etc. These differences are 

 transmitted from one generation to the next. Each plant which 

 breeds differently from the others belongs to a different pure 

 line. A commercial variety then, consists of a mixture of a 

 large number of pure lines which we may designate by the letters 



A, B, C, D, E, F, etc. 



If we select a single plant it will belong to one of these pure 

 lines, for example C. If we multiply the seed of this plant we 

 may have finally a whole field, all the plants of which belong 

 to this pure line C. 



It further follows from this theory that if we again select 

 individual plants from such a pure line field we have still only 

 the same pure line. If we grow the seed of such selected plants 

 in separate rows there is little or no difference between the 

 rows. That is, in selecting and isolating the pure line we have 

 made all the improvement possible in this direction. Theoreti- 



