352 Mendel 's Experiments 



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, with few 

 exceptions, are members of various hybrid series, whose 

 further development in conformity with law is varied and 

 interrupted by frequent crossings inter se. The circumstance 

 must not be overlooked that cultivated plants are mostly 

 grown in great numbers and close together, affording the 

 most favourable conditions for reciprocal fertilisation between 

 the varieties present and the species itself. The probability 

 of this is supported by the fact that among the great array 

 of variable forms solitary examples are always found, which 

 in one character or another remain constant, if only foreign 

 influence be carefully excluded. These forms behave pre- 

 cisely as do those which are known to be members of the 

 compound hybrid series. Also with the most susceptible 

 of all characters, that of colour, it cannot escape the careful 

 observer that in the separate forms the inclination to vary 

 is displayed in very different degrees. Among plants which 

 arise from one spontaneous fertilisation there are often some 

 whose offspring vary widely in the constitution and arrange- 

 ment of the colours, while that of others shows little 

 deviation, and among a greater number solitary examples 

 occur which transmit the colour of the flowers unchanged 

 to their offspring. The cultivated species of Dianthus 

 afford an instructive example of this. A white-flowered 

 example of Dianthus caryophyllus, which itself was derived 

 from a white-flowered variety, was shut up during its 

 blooming period in a greenhouse ; the numerous seeds 

 obtained therefrom yielded plants entirely white-flowered 

 like itself. A similar result was obtained from a sub-species, 

 with red flowers somewhat flushed with violet, and one 

 with flowers white, striped with red. Many others, on the 

 other hand, which were similarly protected, yielded progeny 

 which were more or less variously coloured and marked. 



Whoever studies the coloration which results in orna- 

 mental plants from similar fertilisation can hardly escape 

 the conviction that here also the development follows a 

 definite law which possibly finds its expression in the 

 combination of several independent colour characters. 



