432 



PART III. THE CLASSIFICATION OF PLANTS. 



so that the sporophylls and hypsophylls which it bears are closely 

 aggregated together. Most commonly the flower is ambisporan- 

 giate (monoclinous, or hermaphrodite), but it is frequently mono- 

 sporangiate (unisexual) : in the latter case there are two kinds of 

 flowers, microsporangiate and macrosporangiate, which may be 

 borne by the same individual, when they are said to be diclinous 

 and monoecious; or by two distinct individuals, when they are 

 dioecious (see p. 86). Occasionally the same plant produces both 

 ambisporangiate and monosporangiate flowers, when it is said to 

 be polygamous. The microsporangiate flowers are frequently 

 termed staminate, and the macrosporangiate flowers carpellary 

 (p. 78) : the former are indicated by the sign $ , the latter by 

 the sign ?, and ambisporangiate flowers by the sign ty. In the 

 Gymnosperms the flower is always monosporangiate ; in the An- 

 giosperms it is generally, though by no means always, ambispor- 

 angiate. The flower 

 of the Gymnosperms 

 is nearly always de- 

 stitute of a perianth. 

 The special mor- 

 phology of the Peri- 

 anth is dealt with 

 under the Angio- 

 spermse, in which 

 class it attains its 

 highest develop- 

 ment. 



The Sporophylls 

 are of two kinds : 

 microsporophylls, otherwise known as stamens; and macrosporo- 

 phylls, otherwise known as carpels : the former bear exclusively 

 microsporangia, the latter exclusively macrosporangia. The 

 sporophylls present considerable variety of form, and are on the 

 whole more highly specialised than in any of the Pteridophyta. 



The microsporophyll, or stamen (see p. 78), in its most highly 

 specialised form, consists of a stalk of varying length, the filament, 

 bearing a terminal structure, the anther, which is a sorus of one 

 or more microsporangia embedded in more or less placental tissue. 

 In the less highly organised Phanerogams (e.^.most Gymnosperms), 

 the microsporophylls are morphologically simpler, having the 

 general character of sessile or shortly-stalked scaly leaves. 



FIG. 2S1. Transverse section of a young anther of Sam- 

 bucun racemosa (x80): c the connective with the vascular 

 bundle ; ps the four pollen-sacs (microsporangiaj ; p the 

 mother-cells of the pollen; t tapetal layer; u- the wall of 

 the pollen-sac. 



