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PART III 

 GYMNOSPERMAE. 



The sexual organs are of two kinds. The male organs, 

 viz. the microspores, here called pollen grains, are produced 

 in pollen bags corresponding to the anthers of angio- 

 spermous plants. The pollen bags are borne on special 

 scales called sporophylls, which are arranged either in 

 cones or catkins, but in the highest gymnospermous plant 

 known, viz. Welwitschia, they assume a stamen-like form. 



The female organ, viz. the macrospore, is embedded 

 in a complex body, the whole structure being called an 

 ovule. The ovules are borne either on the edge of leaves 

 as in Cycas (not South African) or on scales, in which case 

 there are generally two on each scale, rarely one only. 

 In a few genera, e.g. Podocarpus, these ovuliferous scales 

 remain isolated, but generally a number of them are 

 aggregated into a cone. The pollen grain, which consists 

 of two or more cells, enters the ovule as a whole (not in 

 the form of a tube), floating in the fluid which fills the 

 micropyle and finally attaching itself to a certain part of the 

 wall of the micropyle (pollen chamber). Here it produces 

 either spermatozoids [Cycas) or a pollen tube, the latter 

 penetrating the tissue of the nucellus and carrying the 

 generative nucleus to the oosphere. 



As a result of the subsequent changes in the nucellus 

 the whole ovule is transformed into a seed. The seed of 

 the gymnosperms consists of three parts, viz. the shell, 

 which is principally derived from the integuments but may 

 be variously modified, the endosperm (nutritive tissue) 

 formed from the prothallial tissue of the nucellus (exc. 

 Gnetum), and thirdly the embryo, the latter being the 

 product of the union of the nucleus of the oosphere with 

 the spermatozoid or the generative nucleus of the pollen 

 tube. The embryo possesses two or more cotyledons. 



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