PRACTICAL BOTAJSTY 



CHAPTER I 

 INTRODUCTORY — PLANTS IN NATURE 



1. Abundance and distribution of plants. We are so accus- 

 tomed to the presence of plant life almost everywhere on the 

 earth that an extreme scarcity of plants over any considerable 

 area seems more remarkable than does their abundance. The 

 complete absence of living plants from any large part of the 

 land surface or the shallower waters is a condition which prob- 

 ably seldom occurs. It may occur in regions where there are 

 poisonous salt deposits, or in times of extreme dryness, or 

 when the temperature is too high or too low for plants to live. 

 Some of the simplest plants can for long periods withstand the 

 most intense cold ever encountered upon the earth, and a few 

 of these plants can withstand high temperatures for a brief 

 time. Ordinarily volcanoes or bodies of hot lava, and some 

 hot springs and alkah deposits are therefore the chief visible 

 portions of the earth which are quite lifeless. 



It is a matter of familiar knowledge that the lands and the 

 waters differ greatly in the density of their plant population. 

 Some areas of the barest Nebraska sand hills do not on the 

 average contain more than one flowering plant to every three 

 thousand square feet, while a weedy garden has been found 

 to contain as many as 75,000 plants in a similar area. If the 

 barest portions of the Sahara were compared with a good lawn 

 or meadow, the disproportion would be far greater. The purest 

 natural waters contain no organisms visible to the eye, while 

 stagnant pools are often so filled with pond scums and other 

 simple and minute plants that each cubic inch contains many 



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