18 



TOBACCO BREEDING. 



protect the flower in the bud. The corolla (b) is the delicately 

 colored floral envelop inclosing the reproductive organs of the flower. 

 Its color tends to attract insects, which are the principal agents in 

 cross-pollination. Next inside the corolla are the five stamens, which 

 are the male reproductive organs of the flower. Each stamen consists 

 of the filament (*), supporting the anther (j) in which the pollen 

 grains (k) are produced. The central organ is the pistil, or female 

 part of the flower. The terminal enlarged portion (g) is the stigma. 



The pollen grains (k) adhere to the 

 k surface of the stigma (g) and germi- 



nate, sending an extremely minute tube 

 (I) down thru the central conductive 

 tissue (h) of the style (/). This tube 

 extends into the cavity of the ovary (d) 

 and finds its way into the ovule (n) 

 thru a small duct or micropyle (m), 

 where fertilization takes place. Other 

 ovules (e) are fertilized by other pollen 

 tubes. These ovules develop into seeds 

 after fertilization. The ovary is two- 

 celled, with a fleshy central placenta 

 (c) on which the ovules are borne. The 

 early capsules mature always before 

 flowering ceases. The shape of the deli- 

 cately colored corolla is somewhat tubu- 

 lar, or, perhaps, more nearly like an 

 elongated funnel. It is comparatively 

 small from the basal end to a point 

 about two-thirds the distance to the ter- 

 minal end of the flower. At this point 

 it enlarges suddenly to more than twice 

 the size of the basal part of the tube 

 (fig. 3). It is composed of 5 petals, 

 which coalesce to form the corolla tube, 

 and separate only at the extreme end. 

 The tobacco flower is symmetrical. The number of sepals and 

 stamens is always the same as the number of petals, but these floral 

 circles do not remain constant, varying rather indefinitely in different 

 strains and even among individuals of the same strain. Trimerous 

 flowers, or flowers with three parts in each flower circle, have been 

 found growing on the same plants with pentamerous flowers, or 

 those having five floral parts. This is the exception, however, and 

 not the rule. 



The tobacco flower is naturally self-fertile, and plants grown from 



Fig. 3.— Diagrammatic sketch of tobacco 

 flower. 



96 



