EXPERIMENTS IN PLANT HYBRIDISATION. 



25 



The figures prescribed for the separate combinations also indicate how 

 many plants with the corresponding colouring belong to the series. Since 

 the total is sixteen, the whole of the colours are on the average distributed 

 over each sixteen plants, but, as the series itself indicates, in unequal 

 proportions. 



Should the colour development really happen in this way, we could 

 offer an explanation of the case above described, viz. that the white 

 flowers and seed-coat colour only appeared once among thirty-one plants 

 of the first generation. This colouring appears only once in the series, 

 and could therefore also only be developed once in the average in each 

 sixteen, and with three colour characters only once even in sixty-four plants. 



It must, however, not be forgotten that the explanation here attempted 

 is based on a mere hypothesis, only supported by the very imperfect result 

 of the trial just described. It would, however, be well worth while to 

 follow up the development of colour in hybrids by similar experiments, 

 since it is probable that in this way we might learn the significance of 

 (the extraordinary variety in the colouring of our decorative flowers. 



So far, little at present is known with certainty beyond the fact that 

 the colour of the flowers in most ornamental plants is an extremely 

 variable character. The opinion has often been expressed that the 

 stability of the species is greatly disturbed or entirely upset by cultiva- 

 tion, and consequently there is an inclination to regard the development 

 of cultivated forms as a matter of chance devoid of rules ; the colouring of 

 decorative plants is indeed usually cited as an example of great instability. 

 It is, however, not clear why the simple transference into garden soil 

 should result in such a thorough and persistent revolution in the plant 

 organism. No one will seriously maintain that the development of plants 

 in the open country is ruled by other laws than in the garden bed. 

 Here, as there, changes of type must take place if the conditions of life be 

 altered, and the species possesses the capacity of fitting itself to its new 

 environment. It is willingly granted that by cultivation the origina- 

 tion of new varieties is favoured, and that by man's labour many varieties 

 are acquired which, under natural conditions, would be lost ; but nothing 

 justifies the assumption that the tendency to the formation of varieties 

 is so extraordinarily increased that the species speedily lose all stability, 

 and their oft'spring diverge into an endless series of extremely variable 

 forms. Were the change in the conditions of vegetation the sole cause 

 of variability we might expect that those cultivated plants which are 

 grown for centuries under almost identical conditions would again attain 

 'Constancy. That, as is well known, is not the case, since it is precisely 

 under such circumstances that not only the most varied but also the most 

 variable forms are found. It is only the Leguminosc?, like Pisunu 

 I'haseolus, Lens, whose organs of fertilisation are protected by the keel, 

 which constitute a noteworthy exception. Even here there have arisen 

 numerous varieties during a cultural period of more than 1,000 years ; 

 these maintain, however, under unchanging environments a stability as 

 great as that of species growing wild. 



It is more than probable that as regards the variability of cultivated 

 plants there exists a factor which so far has received little attention. 

 Various experiments force us to the conclusion that our cultivated plants, 



