250 PLANT RELATIONS. 



ests are the richest known, containing, in addition to the 

 forms enumerated above, such prominent trees as the syca- 

 more, beech, hackberry, honey locust, coffee tree, sugar 

 maple, tulip tree, buckeye, etc. 



In Michigan and Wisconsin the upland forests consist 

 prominently of beech, sugar maple, and hemlock, a charac- 

 teristic mixture of deciduous and evergreen trees ; while 

 the flood-plain forests are scarcely at all developed. 



In the Alleghany region and New England the upland 

 forests are very extensive and complicated, grading from 

 the rich flood-plain forests of the lower levels on the one 

 hand, to the strictly xerophytic forests (pines and black 

 oaks) of the higher levels on the other hand, and dominated 

 by various oaks (especially white, red, and chestnut oaks), 

 chestnuts, and hickories (see Figs. 209, 210). 



The flood-plain forests of New England are not so rich 

 as those of the Alleghany region and Central West, the 

 dominant forms being elms, linden, ash, maples, sycamore, 

 tulip tree, etc. 



173. Tropical forests. — The tropical forests may be 

 grouped under two general heads : (1) the evergreen forests, 

 and (2) the deciduous or monsoon forests. The former are 

 characterized by continuous moisture, and are most largely 

 developed in the East Indies and along the Amazon and its 

 tributaries in South America. The deciduous tropical for- 

 ests are characterized by having a period of relative dry- 

 ness, during which the leaves are shed, and usually border 

 the evergreen forests. 



A. Evergreen forests. — These rainy forests of the tropics 

 may be regarded, as Warming says, " as the climax of the 

 world's vegetation," for the conditions in which they are de- 

 veloped favor constant plant activity at the highest possible 

 pressure. Such great forest growths are found within the 

 region of the trade winds, where there is heavy rainfall, 

 great heat, and rich black soil. So abundant is the precipi- 

 tation that the air is often saturated and the plants drip 



