KAIN-FOREST AND DESERT MOUNTAINS 137 



cloudiness, cause a period of four or five clear rainless days to 

 be an episode of note to the inhabitants of the Blue Mountains. 

 In the Santa Catalinas a period of four or five days of cloudiness 

 and rain is an even greater rarity, and the rainless periods of 

 the lower slopes often last for eight to twelve weeks. In other 

 words the vegetation of the Jamaican mountains is living under 

 a very uniform set of conditions; it enjoys a climate which is 

 practically seasonless, and is able to prosecute its activities 

 throughout the year. To the plants of the Arizona mountains 

 there come the checks of the winter season and the equally sig- 

 nificant checks of the arid seasons; resulting in short periods of 

 great activity and intervening periods of dormancy or of actual 

 injury by drought or cold. 



An ascent of either the windward or the leeward slope of the 

 Blue Mountains will bring to notice a gradual change of flora 

 and of dominant species. On the former slopes there will be a 

 relatively slight change in the general physiognomy of the vege- 

 tation on passing from the warm lowland rain-forests to the cool 

 rain-forest of the mountains, with its lower stature and greater 

 wealth of pteridophytes, brj^ophytes and other pronouncedly 

 hygrophilous plants. On the leeward slopes there is a sharp 

 contrast between the savannas and thorn forest of the coastal 

 plain and the evergreen broad-leaved forest of the lowest hills, 

 but there is only a negligible change in the collective ecological 

 character of the forest from an elevation of 1000 feet to some of 

 the localities as high as 6000 feet. The lack of sharp altitudinal 

 changes of vegetation on the two sides of the island serves to 

 emphasize the unlikeness of these sides when compared with 

 each other at any altitude whatever. The contrast is between 

 a pronounced rain-forest, reeking with moisture, and a relatively 

 open and dry evergreen broad-leaved forest. In short, the un- 

 like moisture conditions of the windward and leeward sides of 

 Jamaica cause a sharper differentiation of vegetation than do 

 the altitudinal temperature differences. In this respect the 

 Santa Catahna Mountains are wholly dissimilar from the Blue 

 Mountains, as they have no major climatic influence causing a 

 difference between any portions of them that lie at the same 



