178 APPLIED BIOLOGY 



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grasses of our lawns and meadows. Such plants are called 

 herbaceous perennials. Many of them are short-lived; 

 for example, farmers know that the best crop of red clover 

 is grown in the first and second years, and after that the roots 

 are unable to produce luxuriant growth of stem and leaves 

 and gradually die out, giving place to grasses and weeds. 

 There are many such cases among plants grown for their 

 flowers. 



Cultivation has changed the duration of life of some plants. 

 A plant which is a perennial in the tropical regions may be 

 an annual in a country with cold winters. Go into any 

 vegetable garden when the frost comes and you will see many 

 plants, such as tomato, pepper, egg-plant, which were started 

 very early in the spring and would have lived much longer 

 if not killed by frost. These are naturally warm-climate 

 plants, but in the temperate zone the winter season limits 

 their duration to a single summer. There are many other 

 examples of changes in duration due to cultivation. Parsnips 

 have been changed from annuals to biennials. Wheat and 

 rye (both annuals) are commonly planted in September, live 

 over the winter, and mature grain in July. Likewise, gar- 

 deners often start annual vegetables and " flowers " in the late 

 autumn, cover them up over winter, and have them mature 

 in early spring or summer. The length of life of such doubt- 

 ful plants could be determined by planting seed in very early 

 spring in order to learn whether the plant will mature seed 

 within a single summer. As an example, certain kinds or 

 varieties of wheat and rye are planted in the spring in the 

 extreme north (Dakota and Manitoba), where cold winters 

 would kill the roots of the winter varieties, and this spring 

 wheat is harvested in the autumn. This could be done where- 

 ever wheat and rye grow ; but the crop is usually not so heavy 

 as with the variety planted in autumn. Also, it is of ad- 

 vantage to the farmer to be able to plant wheat and rye on 

 the same ground after corn is harvested in the autumn, 



