in Hybridisation 321 



differentiating characters, and to deduce the law according 

 to which they appear in the successive generations. The 

 experiment resolves itself therefore into just as many 

 separate experiments as there are constantly differentiat- 

 ing characters presented in the experimental plants. 



The various forms of Peas selected for crossing showed 

 differences in the length and colour of the stem ; in the 

 size and form of the leaves ; in the position, colour, and 

 size of the flowers ; in the length of the flower stalk ; in the 

 colour, form, and size of the pods ; in the form and size of 

 the seeds ; and in the colour of the seed-coats and of the 

 albumen [cotyledons]. Some of the characters noted do 

 not permit of a sharp and certain separation, since the 

 difference is of a "more or less" nature, which is often 

 difficult to define. Such characters could not be utilised 

 for the separate experiments ; these could only be applied 

 to characters which stand out clearly and definitely in the 

 plants. Lastly, the result must show whether they, in 

 their entirety, observe a regular behaviour in their hybrid 

 unions, and whether from these facts any conclusion can 

 be come to regarding those characters which possess a 

 subordinate significance in the type. 



The characters which were selected for experiment 

 relate : 



1. To the difference in the form of the ripe seeds. 

 These are either round or roundish, the depressions, if any, 

 occur on the surface, being always only shallow ; or they are 

 irregularly angular and deeply wrinkled (P. quadratum). 



2. To the difference in the colour of the seed albumen 

 (endosperm)*. The albumen of the ripe seeds is either 

 pale yellow, bright yellow and orange coloured, or it pos- 

 sesses a more or less intense green tint. This difference 

 of colour is easily seen in the seeds as [ = if] their coats 

 are transparent. 



3. To the difference in the colour of the seed-coat. 

 This is either white, with which character white flowers 

 are constantly correlated ; or it is grey, grey-brown, leather- 

 brown, with or without violet spotting, in which case the 

 colour of the standards is violet, that of the wings purple, 



* [Mendel uses the terms " albumen " and " endosperm " somewhat 

 loosely to denote the cotyledons, containing food-material, within the seed.] 



B. H. 21 



