Ch. XIII] 



THE ANGIOSPERMS 



525 



While possessing the distinctive spermatophytie char- 

 acters in common with the Gymnosperms, they differ from 

 that group in some features (Fig. 371) . In the plant body and 

 the tissues the differences are not great, except that the Angio- 

 sperms include ducts in their secondary as well as primary 

 wood, while one great division is endogenous in growth. 



Fig. 371. — The life cycle of an Angiosperm, from various plants. Left, 

 a shoot of Flax (Linum species), with flowers, X 3, and, next, a flower sec- 

 tioned vertically, X \. Right, an anther, cut across, showing four micro- 

 sporangia with microspores (pollen grains), X 6 ; and a pollen grain ungermi- 

 nated, showing vegetative and generative nuclei, and germinated, showing 

 nuclei in the tube, X 110. Below, in longitudinal sections, an ovule, 

 showing prothallial contents of the embryo sac, X 20 ; a young seed, showing 

 young embryo and developing endosperm (prothallus), X 10; and a ripe 

 seed, with embryo embedded in endosperm, X 5. Last, a seedling, X i. 



More considerable differences occur in connection with the 

 reproductive parts. First, the ovules (megasporangia) be- 

 come inclosed by carpellary leaves (megasporophylls), so de- 

 veloped as to form ovary, style, and stigma. Second, the 

 embryo sacs (megaspores), germinate only partially before 

 fertilization, forming instead of the complete prothallus, 

 as in Gymnosperms and lower forms, only the egg cell, two 



