MENDEL 



experts, however, the majority belong 

 to the species Pisum sativimi; while the 

 rest are regarded and classed, some as 

 sub-species of P. sativimi, and some as 

 independent species, such as P. quadra- 

 turn, P. saccharatum, and P. umbella- 

 tum. The positions, however, which 

 may be assigned to them in a classifica- 

 tory system are quite immaterial for 

 the purposes of the experiments in 

 question. It has so far been found to 

 be just as impossible to draw a sharp 

 line between the hybrids of species and 

 varieties as between species and vari- 

 eties themselves. 



DIVISION AND ARRANGEMENT 

 OF THE EXPERIMENTS 



If two plants which differ constantly 

 in one or several characters be crossed, 

 numerous experiments have demon- 

 strated that the common characters are 

 transmitted unchanged to the hybrids 

 and their progeny; but each pair of 

 differentiating characters, on the other 

 hand, unite in the hybrid to form a 

 new character, which in the progeny 

 of the hybrid is usually variable. The 

 object of the experiment was to ob- 

 serve these variations in the case of 

 each pair of 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 sepa- 

 rate experiments as there are con- 

 stantly differentiating characters pre- 

 sented 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 [cotyle- 

 dons]. 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 ap- 

 plied to characters which stand out 

 clearly and definitely in the plants. 

 Lastly, the result must show whether 

 they, in their entirety, observe a reg- 

 ular behaviour in their hybrid unions, 

 and whether from these facts any con- 

 clusion 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. qua- 

 dratwn) . 



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 possesses 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, 

 thr.t of the wings purple, and the stem 

 in the axils of the leaves is of a reddish 

 tint. The grey seed-coats become dark 

 brown in boiling water. 



4. To the difference in the for/n of 

 the ripe pods. These are either simply 



3 [Mendel uses the terms "albumen" and 

 "endosperm" somewhat loosely to denote the 

 cotyledons, containing food-material, within 

 the seed.! 



