236 BREEDING CROP PLANTS 



not known, but there is considerable evidence to substantiate 

 the belief that at least the main types of corn, Zea mays indentata 

 and Zea mays indurata, were cultivated a long time before the 

 discovery of America. 



Table LIX taken from De Candolle (1886) presents a summary 

 of the origin of some common vegetables. 



PEAS 



Some Classification Characters. Considerable historical in- 

 terest attaches' to the pea because of the fact that in studying 

 the inheritance of certain characters in this plant Mendel dis- 

 covered his now famous principles. Garden peas (Pisum sati- 

 vum) are of two kinds, shelling and edible-pod. In the former, 

 seeds only are used as food, while in the latter both pods and seeds 

 may be so utilized. By far the greater part of the garden peas 

 grown belong to the shelling group. Commercial varieties of 

 garden peas are classified on the basis of habit of growth climb- 

 ing, half-dwarf, and dwarf; and length of time to mature early, 

 medium, and late. Peas of the early varieties may be round or 

 wrinkled. Most of the medium and late maturing varieties 

 belong to the sugar peas, which have wrinkled seeds when 

 mature. Size of pod is another important classification charac- 

 ter. Ripened pods may be inflated or somewhat constricted. 



Inheritance. In a reciprocal cross of the varieties Autocrat 

 and Bountiful, it has been suggested (Keeble and Pellew, 1910) 

 that the inheritance of the character tallness involved two factor 

 differences, one for length of internode and one for thickness of 

 stem. In certain crosses White (1918) finds the inheritance of 

 stature still more complicated. Tall varieties (over 4.5 ft.) are 

 divided into three groups and half-dwarfs are separated into two 

 groups. The factorial scheme suggested is as follows : 



FIG. 59. Flower structure of pea. 



1. A single flower a, petals of calyx; 6, side view of corolla. 



2. Front view of fully open flower a, petal of calyx; b, standard; c, whig; d, 

 keel. 



3. The sexual organs removed from the bud. (Adapted from Muller.) a, 

 Filament; b, anther; c, style; d, stigma hairs. 



4. 5. Anthers. 



6. Cross section ovary. 

 9. Longitudinal section ovary. 



Size: 1, %n; 2, Yn\ 3, greatly enlarged; 4, 5, lOOn; 6, greatly enlarged; 

 7, 8n; 8, 40n; 9, 40n. 



