ANGIOSPERMAE 115 



the oosphere of the embryo-sac, hence Engler's name 

 Siphonogama* for Gymnosperms and Angiosperms. 



Under the influence of the male nucleus various 

 changes take place in the oosphere, finally resulting in the 

 formation of the embryo, while the surrounding tissue 

 within the embryo-sac may further develop into a permanent 

 tissue, called the endosperm^, and the nucellar tissue 

 outside the embryo-sac may, although rarely, develop into a 

 similar tissue, called the perisperm (see Fig. 70 and Vol. iv, Fig. 51). 

 Endosperm and perisperm are generally filled with reserve 

 material for the nutrition of the germinating embryo. 

 Often, however, neither endosperm nor perisperm are 

 present, the food materials being stored in the cotyledons 

 of the embryo ; occasionally there are no such reserve 

 materials, e.g. in the case of orchids. 



Classification. 



The natural grouping of angiospermous plants into 

 Monocotyledons and Dicotyledons was recognised very 

 early, having been known a considerable time before 

 Linnaeus. In 1789 Bernard de Jussieu introduced it as 

 one of the principal criterions in his Natural System of 

 Plants, and every later system has retained it in some form 

 or other. Jussieu as well as De Candolle included the 

 gymnospermous plants among the dicotyledons, but when 

 Robert Brown (1827) showed the fundamental difference 

 in the ovules of gymnosperms and angiosperms, the former 

 were separated from the dicotyledons, thus establishing 

 three classes of Flowering Plants, viz. 

 Gymnosperms, Dicotyledons and Monocotyledons. 



It is, however, a far more difficult problem to ascertain 

 the mutual relationship of these three classes. 



In Bentham and Hooker's Genera Plantarum (1862 — 

 1883) and in the Flora Capensis, which is based upon this 



* The few exceptions among some gymnospermous plants, viz. Cycas, would not 

 affect the general suitability of the term. 



-f- This endosperm is not homologous with that of most gymnosperms, though it 

 corresponds in some degree to the endosperm of Gnetum. 



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