140 



MORPHOLOGY 



-P3- 



differ in tlieir structure from those of the Angio- 

 spermia in certain respects. Externally, the ovules 

 have usually one integument; internally, the embryo- 

 sac is formed deeper down in the nucellus, and within 

 the embryo-sac is developed, before fertilization, a 

 mass of tissue or endosperm filling up the embryo- 

 sac. At the micropylar end of the endosperm are 



developed one or more 



ARCHEGONIA (fig. 1 25), 



each of which has a short 

 neck and a ventral por- 

 tion which encloses a nu- 

 cleus. The ventral por- 

 tion with the embedded 

 nucleus is the female cell 

 or oosphere. The pollen- 

 grain falls directly on the 

 micropyle of the ovule, 

 and sends a pollen-tube, 

 which makes its way 

 through the nucellus and 

 the neckof the archegonia. 

 One of the generative 

 cells of the pollen-tube _ 

 fertilizes the oosphere, 



end. 



Fi^. 125. — Macrosporangpium (ovule) of 

 Pinus at Maturity (after Green) 



p,g-y Pollen g:rain. p.t.^ Pollen tube. 

 nuc, Nucellus. em.. Embryo-sac. 

 arch., Archegronia. end.. Endosperm. 



which then changes into 

 an oospore. This oospore develops into an embryo, as 

 in Angiospermia. It should be noted that the endo- 

 sperm in Gymnospermia is formed before fertilization, 

 and not after fertilization, as in Angiospermia. It 

 should be further noted that the development of 

 archegonia is wanting in Angiospermia. Another 

 peculiarity of some of the Gymnospermia also requires 

 special mention. In Cycas revoluta and a few other 

 species of Cycads, as well as in Ginkgo biloba, the gen^ 



