MIGRATIONS OF PLANTS 
ted the tropics as their home; and only under 
the greatest stress of circumstance can they be 
induced to go elsewhere. 
Tropical heat and moisture make for luxur- 
iance of vegetation. There is a much greater 
variety there than in the North. Woody Vines 
climb the tallest trunks, where they intermingle 
their leaves and blossoms with those of their 
host. Gorgeous Air Plants beautify and per- 
fume the forest. Stately Palms wave magni- 
ficent bouquets of pendulous fronds. 
As we travel away from the equator, the vege- 
tation takes on a simpler aspect. ‘There are 
more annuals and more herbs. The number of 
Ferns, Grasses, and catkin-bearing Trees, like 
the Alder and the Birch, increase. The lim- 
ited growing seasons make for a more restric- 
ted accumulation of tissue. Such tropic plants 
as have braved the rigours of the colder climates 
have dwindled much in size. The Castor Oil 
Tree becomes a humble annual (Ricinus Com- 
munis) only three to eight feet in height. Other 
tropical trees become so small that temperate 
zone folk tread them under foot. 
[41] 
