ON BOTANICAL GEOGRAPHY. 281 



Mrs. B. True, but in much less quantity ; herbaceous 

 plants require less heat and more moisture than is to be 

 met with in such climates. The number of ligneous, 

 compared to that of herbaceous plants, universally increa- 

 ses as you approach the equator. 



Emily. Does this increase and decrease proceed in a 

 regular progression from the equator to the poles ? 



Mrs. B. No : the number of annual plants, for instance, 

 is very considerably greater in temperate than in either 

 the tropic or frigid zones. The delicate structure of 

 those plants render them incapable of resisting either the 

 dry heat of the tropics or the severe cold of the polar 

 regions. 



Emily. We have also the advantage of the most beau- 

 tiful and delicate colors in the vegetation of-spring ! while 

 I have heard that, both in the polar and tropical regions, 

 the spring-leaves are of a much darker and more sombre 

 color. 



Mrs. B. Now that you have acquired some idea of 

 what is meant by a botanical region, let us observe how 

 the plants are distributed in one of these regions, and why 

 different plants prefer different localities. 



You will easily understand, that every plant, according 

 to its particular structure, requires the concurrence of 

 many circumstances in order to be brought to perfection. 



Emily. No doubt. It is evident that the same soil, 

 or the same degree of heat, light, or moisture, cannot be 

 equally good for all plants. 



Mrs.B. When plants shed their seed, it is more or 

 less dispersed by wind, rain, or other natural agents, and 

 is finally deposited on a soil which may or may not be fa- 

 vorable to its germination. Thus, in particular spots, a 

 sort of struggle takes place among the different species 

 of vegetables which it produces. The most vigorous 

 plants, and those best suited to the nature of the soil, make 

 the greatest progress, and ultimately exclude the others. 



1515. Of the growth of corn and grasses as well as palms in tropical 

 climates what is Said's 1516. Emily asks if this increase and de- 

 crease proceed in a regular progression from the equator to the poles 

 What is the reply 1 ? 1517. What does Emily say of the color of leaves^ 

 1518. What is needed that a plant be brought to perfection*? 1519. 

 What circumstances, which may be favorable or unfavorable to germi- 

 nation, are mentioned'? 1520. In some particular spots, what takes 

 place among the different species of vegetables'? 



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