CHAPTER XIII 



DIVISION 4. SPERMATOPHYTA: THE SEED PLANTS 



(Phanerogamia : the Phanerogams or Flowering Plants) 



These are the highest plants, and include the great 

 majority of the familiar trees, shrubs, and herbs which 

 constitute the present vegetation of the earth. They are 

 distinguished from the lower divisions by three special fea- 

 tures, all of which have been expressed in names given to 

 the group, viz. by the seed, the flower, and the pollen tube. 

 They comprise some 133,000 species, making over half of 

 the known total of 233,000; and they include the great 

 majority of the plants useful to man. 



The structure of these plants was treated so fully in Part I 

 of this book as to need here only brief mention. The plant 

 body is segregated into leaf, stem, and root, devoted to the 

 photosynthetic formation of food, with flower, fruit, and 

 seed, concerned with reproduction and dissemination. The 

 tissues include the waterproof epidermis with guarded 

 stomata, the bark with lenticels, the photosynthesizing 

 chlorenchyma, the strengthening strands of sclerenchyma, 

 the conducting bundles of vascular phloem and xylem, the 

 growth tissue of meristem including cambium, the storage 

 parenchyma, and the intercellular air system. All of this 

 structure is primarily fitted to a terrestrial life, and the 

 Spermatophytes constitute the characteristic and dominant 

 terrestrial plants. They are, however, more than this, for 

 their relatively high differentiation of structure permits more 

 ready adaptation to special situations, whereby they are 

 enabled to compete with the other groups in their own habi- 

 tats. Thus they have almost wholly displaced the Pterido- 



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