28 Structural Characters: Plants [CH. 



29. Long style and short style in Oenothera. (This 

 difference is probably quite distinct in nature from ordinary 

 heterostylism as seen in Primula, &c.) de Vries (290). 

 The same fact has been observed by Balls (6) in Cotton. 



30. Normal long pollen grains with three pores, and 

 rounded pollen grains usually with two pores. Sweet Pea 

 (Lathyrus odoratus). R.E.C. (20, 21, 22). See Fig. 19. 



31. Normal anthers and sterile anthers. Sweet Pea. 

 R.E.C. (20, 21, 22). 



With regard to these two last features numerous complications occur, 

 which are described in later chapters. 



32. Roundness of seed connected with the presence of 

 starch in large elongated simple grains, and wrinkledness 

 of seed connected with the presence of peculiar compound 

 starch-grains. Pisum. 



This is one of the most familiar of Mendel's original 

 examples (see Fig. 3). It has been re-investigated by 

 many observers. Correns (60) ; Tschermak (269, &c.) ; 

 R.E.C. (20); Hurst (155); Lock (172, 173). The F, seeds 

 made by fertilising an emasculated flower of a wrinkled 

 variety with pollen from a round variety, or vice versa, are 

 generally ordinary round seeds, and /% shows the common 

 ratio 3 round : i wrinkled, the two types being mixed in 

 the pods of the F plants. 



Among the multitude of varieties of peas now cultivated there is a great 

 diversity both of rounds and of wrinkleds. The interrelations of these 

 several types, even as regards seed-shape, have as yet been imperfectly 

 explored. The degree to which the wrinkles are formed is fairly uniform 

 for any one type, but the various types show different degrees of wrinkling. 

 The differences obviously depend chiefly on the chemical and physical 

 properties of the reserve-materials in the cotyledons, and an analysis of 

 these peculiarities might lead to further discoveries. 



Gregory (134) found that the starch in round peas occurs chiefly as 

 large elongated simple grains, whereas in wrinkled peas it is in the form of 

 small grains of irregular shape which are often compounded together (Fig. 9). 

 Darbishire (94) added the interesting fact that in F\ the grains are 

 intermediate, many being large and simple, but round instead of elongated, 

 with an admixture of compound grains. He confirmed also Denaiffe's 

 observation* that wrinkled take up more water than round, but he found 

 that FI is intermediate in this respect, and he suggests that the size, the 



* Denaiffe, Les Pois potagers^ p. 9. 



