434 THE STRUCTURE OF ECONOMIC PLANTS 



The Mature Leaf. — The leaf has an upper epidermis of brick- 

 shaped cells with outer walls that are cutinized. (Fig. 1x4, A.^ 

 Stomata occur in the upper epidermis but are more numerous in the 

 lower. Stomatal counts, per square millimeter of surface, reported 

 by Balls (6) for the vegetative organs are: leaf, upper epidermis, 

 44-97, lower epidermis, 1 16-176; cotyledons, upper epidermis, xoo, 



Fig. L13. A, growing point of cotton stem showing early stages in ontogeny of leaf, 

 stipules, axillary bud, lobes of young leaf, and general topography of tip of mrtin axis, drawn 

 from above and slightly to one side, Pima ; B, later stage in leaf ontogeny, one stipule cut 

 away, Mebane ; C, general topography of fruiting branch terminal, origin of bracts on floral 

 primordium and new axillary primordium. Sea Island ; D, later stage in ontogeny of sym- 

 podial axis showing slightly older floral bracts, Pima; E, later stage than figure D, showing 

 origin of new fruiting branch terminal between leaf and floral primordium, Mebane; F, 

 axillary bud of fruiting branch showing bractlike structure, growing point, leaf and stipule 

 primordia of second node, Mebane; G, early ontogenetic stage of staminal column, petal 

 primordia well differentiated and showing alternate staminal column lobes. Sea Island; H, 

 later stage in ontogeny of staminal column showing stamen primordia in two rows on each 

 ridge, Pima; /, one of five lobes of developing staminal column with stamen primordia, 

 under greater magnification than figure H, Pima ; /, young calyx with bracts removed, 

 Mebane; K, developing petals, Pima; L, young pistil, Mebane. (After Gore.) 



