23° 



ZONES AND REGIONS 



[Pt. Ill, Sect. I 



Gymnospermae. 



Gymnosperms are of quite subordinate significance in the megathermic 

 flora. Coniferae are almost entirely absent ; they are found between the 

 tropics wellnigh only on high mountain chains, outside the tropical climate. 

 Cycadeae (Fig. 117) are a highly characteristic feature of the tropical flora, 

 but are subordinate as regards the number of species and individuals. The 

 species of Gnetum which completely agree with Dicotyledones in their 



Pig. 117. Dioon edule. Mexico. Cerro Colorada, south-east from Jalapa. From a photograph 



by Stahl. 



vegetative organs are also a subordinate and at the same time inconspicuous 

 element in the flora. 



Monocotyledones. 



Monocotyledones supply the most characteristic features of the tropical 

 flora. In the first place, this is true of the Palmac, which however owe 

 their predominance, in tropical landscapes chiefly at any rate, to cultivation. 

 The latter statement is especially true of the coconut palm, Cocos nucifera, 



