CHAPTER' XXIV 



THE ANGIOSPERMS 



THE majority of the Angiosperms, the second subdivision of 

 the Phanerogamia, are easily distinguished from the Gymno- 

 sperms by the possession of flowers, which are really highly 

 specialised fertile shoots. In some cases, however, the flowers 

 are relatively inconspicuous (e.g. Grasses and other wind- 

 pollinated plants), and scarcely conform to the popular notion 

 of these structures. As a matter of fact, the Angiosperms are 

 much more markedly characterised by [the enclosure of their 

 ovules in a protective ovary, as well as by the possession of true 

 vessels and of sieve-tubes of a special type (cf. p. 28). 



The ordinary flower l comprises stamens (microsporophylls) 

 and carpels (megasporophylls) surrounded by one or two series 

 of modified leaves, serving either for protection (calyx) or for 

 the attraction of pollinating insects (corolla). These " non- 

 essential " organs are not uncommonly reduced (e.g. apetalous 

 flowers) or absent (naked flowers, e.g. Hazel). Though the 

 majority of Angiosperms have hermaphrodite flowers, uni- 

 sexuality is not uncommon, the two sexes occurring either on 

 the same (monoecious, e.g. Hazel) or on different plants (dioecious, 

 e.g. Willow). 



In those flowers, which for many reasons are regarded as 

 relatively unspecialised (e.g. Ranunculacese and its allies), the 

 floral axis is elongated, bearing sepals, petals, stamens, and 

 carpels at successively higher levels (hypogynous flowers), and 

 these parts are wholly or in part spirally arranged ; the stamens 

 and carpels, moreover, are usually numerous, and not joined in 



1 The reader is advised to familiarise himself fully with the broad 

 features of floral structure (cf. F. and S., chapters xviii, xix) before passing 

 on to the subsequent matter. 



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