70 PLANT GEOGRAPHY 



beach, some bearing living parasitic Fungi, and among 

 these were numerous fruits of typical Malayan strand- 

 plants. These, from the creeping I pomcea Pe~s-capr& Sw., 

 and Vigna lutea A. Gray, and the " tumble -grass," 

 Spinijex squarrosus L., to Coco-nuts, Pandanus, Barring- 

 tonia, and lofty Casuarina, hung with vines, clothed the 

 island from its shores far up its slopes, the forest-growth 

 being in many places dense. The presence of five species 

 of Ficus is attributed to fruit-eating pigeons, which, 

 though they would probably eject any seeds within three 

 hours of swallowing them, are capable of flying fifty 

 miles in an hour. 



CHAPTER V 



PHYSIOGRAPHIC FACTORS 



THOUGH it is certainly by their influence upon heat, light, 

 rainfall, and drainage that the factors that we have here 

 to consider chiefly influence plants, this influence is so 

 obvious as to demand separate notice. The static, or 

 more permanent physiographic, or topographical factors 

 may be enumerated as altitude, slope, exposure, and 

 surface. Dynamic forces in physiography, such as the 

 weathering of rock-surfaces, their erosion by wind or 

 rain, or the deposition of sediment over a surface, may 

 also obviously cause important changes in the edaphic 

 conditions of habitats. 



ALTITUDE. Altitude, measured generally from sea- 

 level, affects temperature both of soil and air, and thus 

 also the proportion of water that the air can hold without 

 saturation, i.e. precipitation, and the amount of cloud. 

 An important indirect effect is the period during which 

 snow may cover the ground. That vegetation is dis- 

 tributed in zones or belts of altitude was the earliest 

 scientific observation in the history of plant-geography. 

 Mountains in equatorial regions bear successive alti- 

 tudinal zones, belts, or girdles of climate and vegetation, 

 which, at successive elevations, resemble the horizontal 

 zones between the equator and the poles. Dense, hot, 

 wet jungle, or " rain-forest," at their bases, gives way to 

 more open forest, evergreen trees to deciduous, broad- 



