46 Mutability and Individual Variation. 



are just as constant as these. Whether we give them 

 binary and ternary names is not of much consequence. 

 It has always been assumed both before and after Dar- 

 win's time, that they have a common origin, biit in 

 remarkably few cases is there historical evidence that 

 this is so. When and how Datura Stramonium inermis, 

 Rohinia Pseud-Acacia inermis, Lychnis diurna glaber- 

 rima, and the wdiole series of glabrous thornless, white- 

 flowered, laciniate forms, and so forth, have arisen we 

 do not know. They exist and claim recognition equally 

 with the best species. There are a few exceptions, for 

 example Chclidonium laciniatwn Mill. (Fig. Z7 in V, 

 § 25), Fragaria alpina Gaillon (Fig. 7, p. 30), etc., whose 

 source is known. 



In practical horticulture matters are just as bad. End- 

 less varieties are known but only in rare cases is there 

 any historical information as to their origin.^ 



This section of the subject of variability therefore is 

 a purely comparative one, its laws are morphological, 

 and only rarely does it lend itself to historical or experi- 

 mental study. 



2. Polymorphism induced by hybridization is due to 

 new combinations of the heritable characters of the forms 

 crossed. Two groups of phenomena must be distinguished 

 here : scientific experiment and horticultural and agricul- 

 tural crosses. The scientific investigator chooses, if he can, 

 the least 'Variable" species whilst the gardener prefers to 

 cross types of which at least one is very 'Variable." For 

 this variability can be inherited by the hybrid and increases 

 the likelihood of getting new forms ; and this is of coarse 



* (Note of 1908.) A most interesting and complete list of these 

 instances has since been given by Kokschinsky. See Flora, 1901, Bd. 

 59, pp. 240-363. 



