able food, they do not recover from the effects. 

 The effect of food may be observed also in the 

 bee-hive in the production of queens. The 

 term "high living" expresses a condition which 

 produces variations, often called disorders, de- 

 trimental to the best development of organisms 

 whether they be plants or animals. 



(3) Moisture. — This factor in variation is obvious to 



every observer. Botanists classify plants ac- 

 cording to the amount of moisture in their en- 

 vironment into xerophytes, hydrophytes, and 

 mesophytes. Zoologists also classify animals 

 according to their moisture habitat. In the 

 case of crops, moisture in the soil is frequently 

 the limiting factor. The humidity of the air is 

 also an important element in variation produc- 

 tion. 



(4) Temperature. — This factor, a climatic one, is also 



a limiting element inasmuch as protoplasm, the 

 physical basis of life, has its maximum and mini- 

 mum limits of temperature. Within these 

 extremes heat effects mainly the rate of growth, 

 and each species has its own optimum tempera- 

 ture conditions. Certain butterflies assume 

 dimorphic forms to correspond with the season 

 of the year. 



(5) Chemical Agents. — Inasmuch as growth and move- 



ment are the result of the metabolic activity of 

 protoplasm, it is plain that anything that inter- 

 feres with this activity will produce variations. 

 Especially is this true of various chemical 

 agents when they are excluded from or allowed 

 free access to protoplasm. Oxygen, for ex- 

 ample, is essential to the life of protoplasm, but 

 on the other hand there are many kinds of 

 poisons — catalytic, toxic and others, — and se- 

 cretions that modify the activities of living cells 

 and tissues. 



(6) Light. — Light influences living matter in pro- 



ducing chemical effects, in promoting or hinder- 

 ing functional activity, and in its tropic effects. 

 The coloring of leaves, fruit and skin is the re- 

 sult of the chemical action of light; the retarda- 

 tion of growth of stems of plants is the effect of 

 light; and the direction of growth or movement 

 is a tropic effect. 



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