PLANT BREEDING. 39 



with the question of tillering. It is generally supposed that 

 prolific tillering implies high yield, and that the breeder should 

 aim at securing the ma.ximum formation of tillers. But this is 

 not necessarily the case, and it is, in fact, impossible to define 

 with precision the various factors which go to make for a high 

 yield. An attempt is therefore being made to discover what 

 those factors are, how they are inherited, and finally how they 

 may be detected in a single plant or a small number of plants. 

 The chief difficulty is that the cereal plant consists of tillers of 

 different ages, and it has been found by chemical analysis that 

 the tillers act with different efficiencies as factories for the 

 manufacture of food from the soil or the air. Clearly, therefore, 

 the aim of the plant breeder should be to secure a plant with 

 a fair number of strong rapidly-growing tillers, rather than one 

 with a long succession of tillers of different ages and sizes. 

 Several oat varieties now in cultivation fail to yield well because 

 they have numerous lateral tillers which form little grain, and 

 do it at the expense of the strong-growing central tillers. 



Another line of research that is being followed at Cambridge 

 is the investigation of the part played by the root in the living 

 activities of the plant. In the past, plant-breeders have generally- 

 been content to judge a plant entirely from that part of it that 

 is above ground, and have left out of account the part in the 

 soil, on which, in a large measure, the plant depends for its 

 existence. It is possible that some of the failures in breeding 

 may ultimately be found to have been due to the fact that so 

 little attention has been paid to the influence of the root system. 



At Aberystwyth also it has been found essential to investigate 

 principles. One problem now being studied refers to the 

 influence of cutting and methods of cultivating on the spreading 

 of the roots of herbage plants in the soil, and the influence of 

 this root range on the persistency of growth of the plants. 

 The precise effect of external conditions on the growth of Red 

 Clover and some of the chief grasses is also receiving detailed 

 consideration. 



B 4 



