CURIOUS SHAPES 



There are several reasons why these plants took so long to 

 dry up. To begin with, they have inside their stems and 

 leaves certain substances which hold water and delay its 

 escape. Moreover their extraordinary shapes are of very 

 great assistance. They prefer globular, round, circular, 

 pear-shaped, or cylindrical forms. 



Suppose you were to cut such a round mass into thin slices 

 and lay them out flat, it is quite clear that they would cover 

 a much greater surface. Thin leaves also, if squashed up 

 into a round ball, would have a very much smaller surface. 



The water can only escape from the surface exposed, so 

 that these condensed round balls and fleshy columns have 

 far less water-losing surface than ordinary leaves. 



As a matter of fact, it was found by calculation that the 

 surface of an Echinocactus was 300 times less for the same 

 amount of stuff" as that of an Aristolochia leaf. If the 

 actual loss of water from the Echinocactus, as found by ex- 

 periment, was reckoned as one unit per square inch, then the 

 amount of water lost from a square inch of the Aristolochia 

 was no less than 5000 units ! 



This shows that these odd, outrageous shapes of Prickly 

 Pears, Cacti, and other succulents are an extraordinary help 

 to them. We have already pointed out in a previous chap- 

 ter how necessary their spines and prickles are if they must 

 resist rats, mice, camels, and other enemies. 



What we may call the " hedgehog "" type of plant is also 

 very common in desert countries. There are many woody 

 little, much branched, twiggy shrublets, which bristle all over 

 with thorns and spines. They are not at all fleshy, but do 

 with the least conceivable amount of water. 



Another striking characteristic of the desert flora is 

 noticed by every one. Almost every plant is clothed either 



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