CEREAL ADAPTATION AND ASSOCIATION 297 



appear to become antagonistic to each other in a way yet 

 to be explained, but partly, no doubt, from use of the 

 same kinds and quantities of food constituents. There- 

 fore, sometimes a mixture of two crops, such as barley 

 and oats, will produce better results than either one sown 

 alone at the same proportional rate to the unit area. It 

 may be that individuals of the different crops have a stimu- 

 lating effect upon each other. The investigations of the 

 interrelations of crop individuals and their relations as a 

 whole to their environment constitute the applied science 

 of Agronomy. The unit is the crop or plant community. 



321. The stand. The crowding together of indi- 

 viduals in the form of a crop necessitates the considera- 

 tion of questions that are not concerned in the behavior 

 of isolated plants. An important one of these questions 

 is the number of plants to a unit of area, or the stand. 

 The optimum stand is dependent, partly at least, upon 

 the amount of tillering (2, 14), as manifestly every new 

 culm from the same kernel is equivalent to another single 

 culm plant, so long as the single spike or panicle of each 

 is of the same size and quality. The latter condition, 

 however, is probably not always true, for if it were, a high 

 tillering variety would always be undoubtedly desirable, 

 since less space would be required for the same number 

 of spikes. As a matter of fact, it is yet an open question 

 whether, beyond certain limits, a high tillering or a low 

 tillering variety is preferable. There is probably an opti- 

 mum of a medium number of tillers to a plant as well as 

 an optimum stand. 



322. Variation in tillering. There is great variation 

 in the tillering of different cereals and in different cereal 

 varieties. Oats and barley usually tiller less than wheat 

 and rye, and spring varieties of any cereal tiller less than 



