CHAPTER NINE 



HERBS, SHRUBS, AND TREES 



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 

 determine 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 a perennial, because all his plans for handling the 

 crop will depend on this information. Or suppose that an- 

 other man wishes to have a permanent border of flowering 

 plants about his lawn to obstruct the view of some unattrac- 

 tive fields or buildings.- He can choose wisely from among 

 the hundreds of plants listed in nursery catalogs 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 tendency to 

 form single large trunks or a number of stems is helpful also 

 in any study of the structure and processes of stems. 



Longevity of plants. Plants differ greatly in their length 

 of life. To indicate the length of the natural life periods, the 

 terms annual, biennial, and perennial are commonly applied 

 to plants. It is important that these terms be clearly under- 

 stood before the subject of the tissues and their arrangements 

 in stems is taken up, because in each of these length-of-Hfe 

 classes certain characteristics are associated with the form 

 and development of the stem. 



Annuals. Most of our common garden vegetables and 

 field crops are started from seeds in early spring. The seeds 



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