FLORISTIC REGIONS 107 



tidal water is less saline, we have in the east the Nipa- 

 formation, consisting mainly of the " stemless Palm," 

 Nipafruticans Thunb., and, about tide-level, very often 

 a forest in which Barringtonia speciosa L. fil., which has 

 a floating fruit, is the dominant species. 



The tropical forests themselves are divisible, according 

 to the amount of moisture, into four grades : High Rain 

 Forest, High Monsoon Forest, Low Savannah Forest, 

 and Low Thorn Forest. 



High Rain Forest requires over 72 inches of rain annually. 

 Its trees exceed 100 feet in height, are evergreen, and 

 distinctly hygrophilous in type. Though they do shed 

 their leaves periodically, this periodicity is quite inde- 

 pendent of climate or season, and sometimes differs on 

 different branches of one tree. On the other hand, all 

 the plants in a district will, in the case of some species, 

 flower on the same day. Buttress-roots are common, 

 and thick-stemmed lianes, among which are Palms, and 

 the groups mentioned above; and the epiphytes include 

 not only Ferns, Lycopods, and herbaceous plants, but 

 also woody species. 



The Monsoon Forest has from 60 to 72 inches of rain, 

 or more, but with a definite dry season. Its trees are 

 less lofty, tropophilous in character, many of them dis- 

 tinctly deciduous, and the epiphytes do not include 

 woody plants. 



The Low Savannah Forest has generally a rainfall of 

 between 36 and 60 inches a year; but its occurrence 

 depends partly upon edaphic conditions, its soil being 

 necessarily retentive. Its trees are not more than 

 65 feet in height, are rarely evergreen, and distinctly 

 xerophytic in character. Among them may be some 

 with barrel-like water-storing stems, for which the 

 African name "Baobab" may, perhaps, be generalised. 

 Growing in open order, the forest is poor in underwood; 

 but its soil permits the lofty grasses that are so distinctive 

 of savannah conditions; and the trees may bear both 

 herbaceous lianes and epiphytes. 



The Thorn Forest, for which some authors would 

 employ the Brazilian name " Caatinga," with even less 

 rainfall and a non-retentive soil, is even more markedly 

 xerophytic in the generally thorny character of both its 

 trees and their undergrowth, and in the general absence 

 of all epiphytes. 



