in Hybridisation 83 



most variable forms are found. It is only the Leguminosos, 

 like Pisum, Pkaseolus, 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 1000 years ; these 

 maintain, however, under unchanging environments a sta- 

 bility 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, with few ex- 

 ceptions, are members of various hybrid series, whose 

 further development in conformity with law is changed and 

 hindered 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 

 develop precisely as do those which are known to be members 

 of the compound hybrid series. Also with the most sus- 

 ceptible 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 arrangement of the colours, while others furnish forms of 

 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 



62 



