CHAPTER IV 

 THE VEGETATIVE STRUCTURES 



It is convenient to treat separately the vegetative 

 and reproductive phases of a plant's life-history; but 

 as a matter of fact vegetative structures often reproduce 

 the plant, and reproductive structures do vegetative 

 work. We shall consider first the typically vegetative 

 structures, the trunk, or stem, the leaf, and the root; 

 and then the typically reproductive structures, the cones 

 and gametophytes, which lead up to the formation of 

 seeds. 



THE STEM 



It is the unbranched trunk and the crown of leaves 

 which make the cycads look like tree ferns or palms. 

 The remote ancestors of the cycads, now entirely extinct 

 but fairly well known from leaf impressions and fossils 

 of the Paleozoic age, are called the Cycadofilicales, the 

 name indicating a combination of cycad and fern 

 characters. The leaves of these ancient forms were so 

 identical with those of ferns that botanists called the 

 Paleozoic the ''Age of Ferns," until it was found that 

 most of the leaves belonged to these primitive seed 

 plants. In many cases it is not yet known whether a 

 given leaf is that of a fern or of one of these remote 

 ancestors of the cycads. The leaves look like those of 

 ferns, they have the same internal structure, and it is 

 beyond dispute that the plants are simply ferns which 

 have developed the seed habit. For the sake of con- 

 venience we have made a definition separating the ferns 



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