DESCKIPTIVE TEEMS 



363 



secretion of volatile oils by the petals or other floral parts, while 

 the nectar is secreted by nectar glands, usually located at the 

 base of the pistils on the receptacle. In addition many flowers 

 possess the power of movement in the stamens and pistils 

 by which the anthers and stigmas are either separated or 

 approximated when ripe, thus insuring either close-pollination, 

 cross-pollination, or self-pollination. 



Pistils, seeds, and fruits. Pistils are either simple or com- 

 pound, according as they are composed of one or more spo- 

 rophylls, or carpels. Simple pistils are composed of one carpel, 



'Stigma" 

 Carpel^ 



Placenta 

 Ovary 



FIG. 220. Simple and compound pistils 



A, simple pistil with one carpel; B, compound pistil with two carpels and central 

 placenta ; C, compound pistils (a, with parietal placentae ; b, c, with central placenta) 



or megasporophyll, as in the mandrake, bean, and locust 

 (Fig. 220, A). Compound pistils are composed of two or more 

 carpels, or sporophylls, so united as to inclose one or more seed 

 cavities, or locules (B). The placentae, or lines of attachment of 

 the ovules, may be either central or parietal (.C'). 



Ovules are of three main types, according to their form and 

 the relation of the ovule proper to the funiculus. Orthotropous, 

 or straight, ovules grow straight, without curvature, from the 

 funiculus, or stalk. Campylotropous ovules are curved, owing 

 to the greater growth of one side of the ovule during its 

 development, as in Capsella (Fig. 203, (7). Anatropous ovules 

 are the most common type, in which the ovule becomes com- 

 pletely inverted during its early development and adheres to 



