CHAPTER SEVENTEEN 



LONGEVITY OF HERBACEOUS AND WOODY STEMS 

 Every one who has occasion to grow plants needs to know 

 something about the length of life of the plants he is concerned 

 with, and he must know also whether they have herbaceous or 

 woody stems. For example, suppose a farmer wishes to deter- 

 mine whether it will be more profitable to grow sweet clover or 

 alfalfa in a certain field. Before planting either of these crops, 

 he should know that one of them is a biennial and the other 

 perennial, because all his plans for handling the crop will depend 

 on this information. Or suppose that another man wishes to 

 have a permanent border of flowering plants about his lawn to 

 obstruct the view of some unattractive fields or buildings. He 

 can choose wisely from among the hundreds of plants listed in 

 nursery catalogues only when he has definite information about 

 the longevity of the plants and as to whether they are herbs, 

 shrubs, or trees. A clear understanding of the classification of 

 plants on the basis of their length of life, their woodiness, and 

 their habit of forming single large trunks or a number of smaller 

 stems is helpful ; also in any study of the structure and processes 

 of stems. Plants differ greatly in their length of life. To indi- 

 cate the length of the natural life periods, the terms annual, bien- 

 nial, and perennial are commonly applied to plants. 



Annuals. Most of our common garden vegetables and field 

 crops are started from seeds in early spring. The seeds germinate ; 

 roots and shoots develop ; and by midsummer or autumn, 

 flowers and fruits are produced and new seeds, which contain the 

 beginning of another generation of plants, are formed. Then the 

 plants die. The period from seed^germination to seed production 

 and death is called the life period. If it is completed within a 

 single growing season, the plant is called an annual (Latin : annus, 

 year). Corn, lettuce, radishes, beans, pumpkins, morning- 

 glories, and ragweeds are familiar annual plants. 



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