148 



BOTANY 



size of plants decreases as we approach the line of perpetual snow. The 

 largest trees occur at the base of the mountains; the same species of trees near 

 the summit appear as mere shrubs. Continued cold and high winds are evi- 

 dently the factors which most influence the slow growth and the size and 

 shape of plants near the mountain tops. Cold, Httle light during the short 

 days of the long winter, and a slight amount of moisture all act upon the 

 vegetation of the arctic region, tending toward very slow growth and dwarfed 

 and stunted form. Trees over five hundred years old have been noted in 

 cold regions with trunks less than three feet in diameter at the base. 



Conditions in a moist, semi-tropical forest. The so-called " Florida moss " is a flowering 

 plant. Notice the resurrection ferns on the tree trunk. 



Vegetation of the Tropics. — A rank and luxuriant growth is found in 

 tropical countries with a uniformly high temperature and large rainfall. In 

 general it may be estimated that the rainfall in such countries is at least 

 twice as great as that of New York state, and in many cases three to four 

 times as great. An abundant water supply, together with an average tem- 

 perature of over 80° Fahrenheit, causes extremely rapid growth. One of the 

 bamboo family, the growth of which was measured daily, was found to in- 

 crease in length on the average nearly three inches in the daytime and over 

 five inches during each night. The moisture present in the atmosphere 

 allows of the growth of many air plants (epiphytes), which take the 

 moisture directly from the air by means of aerial roots. 



