420 GENERAL BOTANY 



the bulbs, tubers, or rhizomes facilitates the rapid growth of 

 aerial shoots and flowers during the short rainy season. In tem- 

 perate regions the wild species often inhabit hillsides or banks 

 where dry conditions are imposed during the summer months. 

 Commercial importance. This habit of producing underground 

 stems facilitates the cultivation of the Liliaceae for commercial 

 purposes, since the bulbs, corms, and rootstocks thus produced 

 allow of shipments and long storage, which would otherwise be 

 impossible. Tulips and hyacinths, for example, are grown in 

 Holland for shipment to this country. The bulbs arise as lateral 

 buds which produce the young bulbs or offsets in considerable 

 numbers each year from the mother bulbs (Fig. 79). Ten or 

 twelve daughter bulbs are produced from one mother tulip bulb 

 in a season, and as many as twenty or more from a hyacinth 

 bulb. These offsets are grown for from three to five years, then 

 dried and shipped to various parts of the world for the growth 

 of flowers for ornamental and decorative purposes. The biologi- 

 cal and commercial history of the narcissus, lilies, onions, and 

 other ornamental and food-producing varieties of the lily family 

 is very similar to that briefly sketched for the tulip and the hya- 

 cinth. Most of these species have been greatly improved, as 

 regards variation in color and size, by hybridization ; but the 

 perpetuation of such variation must be secured by vegetative 

 reproduction, as we learned earlier in the study of reproduction, 

 hybridization, and breeding. 



SMIL AGIN A AND EEYTHEONIUM 



Habitat and habit. The species of Smilacina usually inhabit 

 wooded slopes in the shade of trees, where a considerable amount 

 of humus is present in the soil. They represent those species of 

 the Liliaceae which have both an underground and an aerial stem, 

 with the usual differentiation in function between the two kinds 

 of stems. The aerial stem bears the leaves and the cluster of 

 flowers of the summer season, while the underground stem serves 

 for food storage, conduction, and the formation of buds for the 

 next season's growth (Fig. 267, A). During dry periods, and in 



