Principles of Heredity 167 



course of three or four years (the shortest time which I have 

 ascertained it takes to attain the climax of variation in the 

 produce of cross-fertilised peas, and until which time it would 

 seem useless to expect a fixed seedling variety to be produced*), 

 although a reversion to the characters of either parent, or of 

 any one of the ancestors, may take place at an earlier period. 



These circumstances do not appear to have been known to 

 Mr Knight, as he seems to have carried on his experiments by 

 continuing to cross his seedlings in the year succeeding their 

 production from a cross and treating the results as reliable ; 

 whereas it is probable that the results might have been materially 

 affected by the disturbing causes then in existence arising from 

 the previous cross fertilisation, and which, I consider, would, in 

 all cases where either parent has not become fixed or permanent, 

 lead to results positively perplexing and uncertain, and to varia- 

 ations almost innumerable. I have again selected, and intend 

 to sow, watch, and report ; but as the usual climax of variation 

 is nearly reached in the recorded experiment, I do not anticipate 

 much further deviation, except in height and period of ripening- 

 characters which are always very unstable in the pea. There 

 are also important botanical and other variations and changes 

 occurring in cross-fertilised peas to which it is not my 

 province here to allude; but in conclusion I may, perhaps, in 

 furtherance of the objects of this paper, be permitted to inquire 

 whether any light can, from these observations or other means, 

 be thrown upon the origin of the cultivated kinds of peas, 

 especially the " maple " variety, and also as to the source whence 

 the violet and other colours which appear at intervals on the 

 seeds and in the offspring of cross-fertilised purple-flowered peas 

 are derived." 



The reader who has closely followed the preceding 

 passage will begin to appreciate the way in which the new 

 principles help us to interpret these hitherto paradoxical 

 phenomena. Even in this case, imperfectly recorded as it 

 is, we can form a fairly clear idea of what was taking place. 



* See later. 



