SPERM ATOPH VTA 



409 



Gymnospermae 

 Plants woody 



Wood without vessels (except in Gnetales) 

 Sporophylls borne in strol)ili (except in 



Cycadofilicales) ; perianth absent 

 Ovules freely exposed, not in a closed ovary 



Female gametophyte with abundant vege- 

 tative tissue and with archegonia (ex- 

 cept in Welwitschia and Gnetum) 



Pollen coming in direct contact with ovules 



Male gametophyte usually with one or 

 more prothallial cells; generative cell 

 producing a stalk cell and a body cell, 

 the latter giving rise to two male cells 

 that may or may not be organized as 

 ciliated sperms 



Endosperm formed from vegetative tissue 

 of female gametophyte 



Development of embryo initiated by free- 

 nuclear division (except in Welwitschia 

 and Gnetum) 



Cotyledons two to many 



Angiospermab 



Plants woody or herbaceous 



Wood almost always with vessels 



Sporophylls borne in flowers; perianth 

 generally present 



Ovules in a closed ovary formed by one or 

 more megasporophylls 



Female gametophyte with little or no 

 vegetative tissue, consisting typically 

 of an eight-nucleate embryo sac ; arche- 

 gonia absent 



Pollen not coming in direct contact with 

 ovules 



Male gametophyte without prothallial 

 cells; generative cell directly producing 

 two male cells that are never ciliated 



Endosperm arising after fertilization, gen- 

 erally from a triple fusion of nuclei 



Development of embryo without a free- 

 nuclear stage 



Cotyledons one or two 



GENERAL CONCLUSIONS 



The two most outstanding features of the spermatophytes are the 

 presence of seeds and the development of the flower. They excel the 

 pteridophytes in the complexity of their vegetative organs, while the 

 gametophyte is subordinated to the sporophyte to such an extent that it is 

 always dependent upon it. The microsporangia and megasporangia are 

 borne by sporophylls that, with few exceptions, are considerably less leaf- 

 like than the sporophylls of most pteridophytes. Almost invariably the 

 megasporangium (nucellus of the ovule) produces only one functional 

 megaspore, which always gives rise to the female gametophyte without 

 being shed. In all spermatophytes the development of the sporangia is 

 eusporangiate, as among the lower pteridophytes, but the initials are 

 hypodermal rather than epidermal in origin. 



In gymnosperms the archegonia are more reduced than in pterido- 

 phytes, while in angiosperms they are eliminated. The male gameto- 

 phyte produces only two sperms, or male cells, and true antheridia are not 

 present. Among existing groups, ciliated sperms occur only in the Cyca- 

 dales and Ginkgo. Fertilization, accomplished with the aid of a pollen 

 tube, results in an embryo that develops inside the ovule. 



The Seed. The adaptation to life on land is more nearly perfect in the 

 spermatophytes than in any other group of plants. This has come about 



