Hayes and Garber - Cucurbit Breeding

236 BREEDING CROP PLANTS
not known, but there is considerable evidence to substantiate
the belief that at least the main types of corn, Z'ea 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 interest
attaches to the pea because of the fact that in studying
the inheritance of certain characters in this plant Mendel discovered
his now famous principles. Garden peas (Pisum sativum)
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 climbing,
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 character.
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 :
keel.
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, wing; d,
3. The sexual organs removed from the bud. (Adapted from Mutter.) a,
Filament; 6, anther; c, style; d, stigma hairs.
4. 5. Anthers.
6. Cross section ovary.
9. Longitudinal section ovary.
Size: 1, %n; 2, %n; 3, greatly enlarged; 4, 5, lOOrc; 6, greatly enlarged;
7, 8n; 8, 40n; 9, 40n.