CHAPTER VIII 



THE PROBLEMS OF PLANT DIS- 

 TRIBUTION 



THE origin of the existing flora of the earth 

 is lost in the obscurity of an enormously re- 

 mote past. We have practically no knowledge of 

 the lower plant types from the earlier geological 

 formations, which is not surprising when we re- 

 member the extreme delicacy of these very perish- 

 able organisms; and the first plant remains that can 

 be identified belong to species relatively high up in 

 the scale of development, and must have been pre- 

 ceded by countless forms of lower rank. 



Antiquity of the Principal Types of Plants. It is 

 evident from a study of the fossils of the Paleozoic, 

 that nearly all of the living plant types, except the 

 highest forms of seed-plants, were already in exist- 

 ence during that period. Ferns and primitive seed- 

 plants occur in the Devonian, and these reach a 

 high degree of development during the Carbonif- 

 erous. While few traces of the less resistant plant 

 types, such as the seaweeds and mosses, are met 

 with, enough of these have been found to show, as 

 might have been expected, that these plants also 

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