334 Introduction to Botany, 



For the greater part of the tropics there is a wet and a 

 dry season, the wet season occurring in summer ; but the 

 dry season in many places is not without rains. 



On account of the uniformly high temperature and 

 abundance of moisture, plants make a phenomenal growth 

 in the tropics. It is recorded, for instance, that a shoot of 

 Bambusa grew nearly 8 meters within a single month, and 

 that a Dendrocalam7ts {Yig. i8o) increased in length on the 

 average 'j.y millimeters during the daytime and 13 milli- 

 meters during the nighttime of each day. 



On account of the moist atmosphere many kinds of epi- 

 phytes flourish in the tropical forests, sometimes growing 

 so luxuriantly as to break off the branches of trees with 

 their weight (Fig. 16). Besides the epiphytes, the plants 

 which characterize the vegetation of the tropics are the 

 palms, bamboos, many species of climbing plants, and tree 

 ferns. The luxuriant character of a tropical forest is well 

 shown by Fig. 181. 



In regions where the dry season is well pronounced, trees 

 shed their leaves at that time just as they do in the tem- 

 perate zones in winter, but where the rainfall occurs 

 throughout the year, and everywhere along water courses, 

 the leaves are not as a rule all cast off at once, but are 

 shed gradually and from different branches at different 

 times. At any season in such regions trees may be seen 

 with leaves, flowers, and fruits in various stages of devel- 

 opment. 



The damp atmosphere of the forests in regions where 

 rainfall is frequent throughout the year does away with 

 the necessity of thick layers of cork as a protective 

 covering for the bark, and the trunks of trees are, in con- 

 sequence, relatively smooth and frequently green in color. 

 To the thinness of the bark is probably due the pecuHar 



