44 THE GEOGRAPHY OF PLANTS. 



most characteristic plants seen in the zone, 

 The immense size of some of the trees of this 

 region excites universal astonishment. The 

 Baobab, or monkey-bread, (Adansonia digitata,} 

 a native of Senegal, Cape de Verd Islands, 

 Egypt, and Nubia, is one of tlie most gigantic 

 trees known. The trunks of this species are 

 found of the enormous size of from seventy to 

 one hundred feet in circumference ; the spread 

 of the branches is extensive ; main roots have 

 been traced to the distance of one hundred feet 

 from the main stem. The height of these 

 enormous stems is not by any means in pro- 

 portion to their size, frequently not much ex- 

 ceeding their diameter, this being often thirty- 

 four feet, while the tree itself is rarely more 

 than fifty or sixty feet high. It covers the 

 sandy plains so entirely with its umbrella-shaped 

 top, that a forest of these trees presents a com- 

 pact surface, which at some distance seems to 

 be a green field. Cape Verd has its name 

 from the numbers that conceal the barren soil 

 under their spreading tops. The hollow r trunks 

 of the baobab are often so capacious, that several 

 negro families will take up their abode in one. 

 The gigantic size of these trees has often 

 astonished the traveller, and has led to investi- 

 gations with regard to their probable age. It 

 is known to most observers, that the principal 

 forest trees (in our own country, all) increase 

 by coatings from -without, and that the concen- 

 tric rings visible on cutting across the stem, 

 afford an indication of the age, each ring being 



