THE EVOLUTION OF PLANTS 



203 



margins, suggesting a xerophytic or halophytic habitat. 

 The stem in the lower portion gave rise to numbers of 

 slender roots, some of which appear to have been aerial 

 in their origin. These grew downward and often branched 

 where they entered the soil. 



FIG. 87. Young leaf of the Cycad, Bowenia serrulata. Comparison 

 of this with a leaf of the fern Angiopteris (Fig. 88) shows how difficult 

 it might be to decide from a fossil leaf whether the plant was a cycad or a 

 fern. (C/., also, Fig. 91.) (Photo from specimen in Brooklyn Botanic 

 Garden.) 



"The stems, roots, and petioles, and even the pinnules, 

 have been found calcined and so beautifully preserved 

 that their entire structure can be made out with certainty. 

 Without going into a technical description of these organs, 

 it may be said that the stem when young, and before 

 secondary growth has begun, has a very strong resemblance 



