1798 A TEXTBOOK OF THEORETICAL BOTANY 



several of which have been grown on a commercial scale in different parts 



of Africa. 



Finally we come to the genus Gossypium, which is by far the most 

 important economically. Species of Gossypium provide the Cotton of 

 commerce, which is obtained from the hairs covering the seeds. The 

 cotton plant is naturally a perennial shrub or a small tree but is generally 

 grown as an annual. The flowers vary in colour but are generally white_or 

 yellow in the American, yellow with crimson spots in the Egyptian, and 

 purplish red in the Indian varieties. A number of different species are 

 involved therefore in the production of cotton and we shall consider the 

 matter more closely in Volume IV. In the meantime, we may note that 

 G. harbadense is the Sea-Island Cotton, G.peniviamim is the South American 

 Cotton, G. hirsiitum the Short Staple Cotton, G. herhaceum is the East 

 Indian Cotton and G. arbor eiim is the Tree Cotton of tropical Africa. It 

 must be pointed out however that some confusion has existed regarding 

 the identity and limits of these species and most of the forms now in culti- 

 vation are hybrids. 



SAPINDALES 



The Sapindales are Archichlamydeae with the following characters. 

 The flowers are usually actinomorphic. The sepals are imbricated or occa- ■• 



sionally valvate, petals are usually present and imbricated in the bud. The ' 

 ovary is superior, with one or two ovules in each loculus, and the seeds may 

 or may not have endosperm. The plants are mostly trees or shrubs, with 

 non-glandular leaves which may be either simple or compound. 



This order, as originally defined by Engler, is obviously not a very 

 united one and most modern authors subdivide it into two distinct orders 

 by relegating a number of the families into a separate order, the Celastrales. 

 This method is followed by both Rendle and Hutchinson. According to 

 this later and better system the arrangement of the principal families is as 

 follows : 



Sapindales: Anacardiaceae, Sapindaceae, Aceraceae, Hippoca- 



stanaceae. 

 Celastrales: Celastraceae, Aquifoliaceae, Staphyleaceae, Empetraceae. 



The Sapindales in this more restricted conception are trees or shrubs 

 with compound leaves and numerous flowers. These flowers are either 

 unisexual or bisexual, actinomorphic or less often zygomorphic, hypogynous 

 and generally pentamerous. The ovary is composed of two or three carpels 

 with one or two ovules in each loculus. The embryo is large and endosperm 

 -is absent. The Celastrales on the other hand are trees or shrubs with simple 

 leaves and whitish flowers. The flowers are usually bisexual, either tetra- 

 merous or pentamerous and actinomorphic. The ovary is plurilocular, con- 

 taining one or two ovules in each loculus. The embryo is small within a 

 fleshy endosperm. 



