236 BOTANY OF CROP PLANTS 



though the reverse is sometimes the case. The inner circle 

 of stamens is the first to shed pollen. 



Fruit. — This is a three-celled, membranaceous capsule 

 with locuHcidal dehiscence. Two seeds, black in color, 

 are usually borne in each locule of the capsule. The seeds 

 (Fig. 92) are convex on one side and almost flat on the other, 

 and possess a large quantity of oil. The embryo is cylin- 

 drical and curved. 



Germination of Seed, and the Seedling. — At the beginning 

 of germination, the primary root is forced out by the growth 

 of the curved end of the embryo (Fig. 92). The curved 

 end of the embryo, the cotyledon, comes out of the ground 

 in the form of a closed loop. The tip of the cotyledon re- 

 mains attacked to the endosperm and seed coat. When the 

 soil is loose, the endosperm and seed coat may be pulled 

 from the ground, but in case it is compact, they remain 

 beneath the ground. The cotyledon absorbs nourishment 

 from the endosperm. When this is used up, the cotyledon 

 tip withers and becomes detached from the seed coat. At 

 the base of the cotyledon, where it joins the hypocotyl, there 

 early appears a longitudinal sHt; through this, the first 

 foliage leaf emerges. The cotyledon later disappears 

 entirely. 



Geographical. — There are about 250 species of the genus 

 Allium, the majority of which occur in boreal America, 

 Mexico and northern Europe. A number are also found in 

 Abyssinia and extratropical Asia. The cultivated onions 

 require cool, moist weather during the early stages of their 

 development, but ripen better if the weather is drier. 



Key to Principal Cultivated Species of Genus Allium 



Leaves flat and solid (Fig. 90). 



Leaves keeled, very narrow, Allium salivum (garlic). 

 Leaves keeled, very broad, Allium porrum (leek). 



