CHAPTER XVIII 



SPERMATOPHYTES (SEED PLANTS) 

 Gymnosperms (seed not enclosed) 



Spermatophytes or Seed Plants constitute the fourth large 

 division of plants. They are the most highly developed plants, 

 and, therefore, in them we find the final achievement of plant 

 evolution. Their distinguishing feature is the seed, although 

 they have other notable features not found in the groups pre- 

 viously studied. The notable features of Pteridophytes, such as 

 sporophylls, strobili, heterospory, dependent gametophytes that 

 are developed within the spore wall, and the retention of the 

 megaspore in the megasporangium, are retained by the Sperma- 

 tophytes and to these the'y have added new features. Because 

 of the seed, lumber, fibers, and numerous other products ob- 

 tained from them, the Spermatophytes surpass all other divisions 

 of plants in economic importance. They are also very numerous, 

 and on account of the large size of their sporophytes they are our 

 most conspicuous plants. 



The Spermatophytes are divided into two groups, the Gym- 

 nosperms and Angiosperms. As the names suggest, the Gym- 

 nosperms bear their seeds exposed while Angiosperms bear them 

 enclosed, but the two groups differ also in other features as will 

 be noted later. 



The Gymnosperms are more primitive than the Angiosperms 

 and are, therefore, more like the Pteridophytes, the group from 

 which Seed Plants are supposed to have originated. The groups 

 of Gymnosperms most like Pteridophytes are now extinct and 

 hence are known only by their fossils. Some of these extinct 

 forms resembled Ferns so much that they are called Pterido- 

 sperms, a term which means " Ferns with seeds." Thus Gymno- 

 sperms connect more closely with the Pteridophytes than the 

 latter group does with the Bryophytes. The Gymnosperms still 

 in existence are divided into a number of groups, but a study of 

 the Cycads and Pines will give a notion of the general features 

 characteristic of Gymnosperms. 



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