292 Practical Hints [ch. 



Rogiteing. 



The Introduction of these ideas will help much by showing 

 what is to be expected of a pure variety. I may give an 

 example. Hitherto, when in growing seed-crops, unde- 

 sirable " rogues " recur continually through long periods of 

 years, the fact has been accepted as part of the natural 

 perversity of the variety. The grower devotes much time 

 and expense in keeping the rogues down, but the idea that 

 they can be got rid of altogether does not generally occur 

 to his mind. Nevertheless in many such cases Mendelian 

 observation at once provides the means of carrying out 

 this radical treatment with success. I cannot here discuss 

 the intricate question of the reality and signification of that 

 degeneration of cultivated varieties which is believed to 

 occur generally and certainly occurs sometimes when selec- 

 tion is suspended. All that we can insist on at this stage 

 of the inquiry is the fact that much of the Irregularity of 

 crops which passes for such natural degeneration is readily 

 preventlble. 



The rogue-plants may be of various kinds, and their 

 nature must be separately determined in each case. For 

 example, they may be recesslves merely, and if so they can 

 be eliminated by breeding from pure dominant individuals, 

 according to the system now well understood. It is possible 

 also that they may owe their existence — If the plants are 

 fertilised by insects — to special combinations of comple- 

 mentary characters. In that case, to exclude the possibility 

 of their production must be a more difficult, though not 

 necessarily a hopeless task. But in the light of present 

 knowledge one definite and conspicuous conclusion has 

 been attained, that for the appearance of each type in a 

 crop there must be some specific and usually ascertainable 

 cause ; and an aim of practical seed-growers should in future 

 be to search carefully for such causes. When this search 

 is made, the guess may even be hazarded with some con- 

 fidence that in numerous examples the cause of Impurity in 

 seed-crops will often be found to be nothing more recondite 

 than an unsuspected admixture of another variety, the seeds 

 of which are overlooked as apparently belonging to the 

 selected type. In a certain strain of eating peas I have 



