180 THE SMALL GRAINS 



produced both white-chaffed and brown-chaffed plants. 

 There are many other similar instances. In some cases 

 the mixture is so even that it is difficult to decide which 

 type is the one intended in the introduction, and occasion- 

 ally some other type than the one intended proves to be 

 the best one of the mixture. Sometimes different species 

 or subspecies are represented in a single introduction. 



The standard varieties of the country, whatever their 

 origin, are commonly found mixed on the farm. Even 

 if descended from a pure strain, they soon become mixed 

 through thrashing operations, and from using more than 

 one variety on the same farm. The re-sorting of mixtures 

 again and again, and re-distribution of good seed, will 

 probably always be a large part of the agronomic work 

 of the experiment stations. 



177. Roguing is the operation of eradicating foreign 

 plants from the standing crop ; for example, the practice 

 of cutting rye out of wheat. It differs from sorting, in 

 that the latter is done on a smaller scale and not usually 

 in the standing crop. It differs from weeding, in the 

 fact that only foreign plants of the same or allied species 

 are involved, such as the eradication of wild oats from the 

 oat field, or of awned wheat from a field of awnless wheat. 

 This is one of the few crop improvement operations that 

 the farmer himself can and sometimes will perform. 



178. Cleaning and grading. These two operations 

 may usually be performed by the same means, and at the 

 same time, and are therefore discussed together. They 

 are on the border line between actual selection and simple 

 mechanical conditioning or purifying, but the same air 

 blast, for example, that drives away chaff, dirt, and weed 

 seeds will also blow out many shriveled and small light 

 seeds of the crop under treatment. There are three 



