CHAPTER VI 

 PTERIDOPHYTES 



THE FIRST VASCULAR PLANTS 



53. Recapitulation. The history of the plant kingdom 

 has been followed from the Algae, exposed to water, to the 

 Liverworts, exposed to air. From the Algse the dependent 

 Fungi seem to have come, and together the two groups con- 

 stitute the Thallophytes, the lowest great division of plants. 

 From the Algse the Liverworts also came by acquiring the 

 land habit, and in turn gave rise to Mosses, and Liverworts 

 and Mosses together constitute the Bryophytes, the second 

 great division of plants. In the Bryophytes the body is more 

 complex than in the Thallophytes, is related to air exposure, 

 and alternation of generations is established. In this alter- 

 nation the gametophyte is the independent generation, dis- 

 playing the green tissue and bearing the sex-organs ; and the 

 sporophyte is a dependent generation. In such Liverworts 

 as Anthoceros, however, the dependent sporophyte has ad- 

 vanced far towards independence, as shown by its develop- 

 ment of abundant green tissue, which makes the sporophyte 

 only partially dependent. Therefore, it seems probable that 

 the Liverworts gave rise not only to the Mosses, but also to 

 the third great division of plants (Pteridophytes), with its 

 completely independent sporophyte. It is important, there- 

 fore, to examine the structure of the independent sporophyte, 

 for it involves much more than the appearance of green 

 tissue. 



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