114 A TKXTBOOK OF BOTANY [Ch. IV, 1 



bark, are brown or gray, as tli(^ incklental result of the 

 weathering-decay of the tissues. 



Stems differ much in duration, according to the habits of 

 the plant. Some are annuals, that is, they start from seed, 

 develop an herbaceous shoot, use tlieir food to make new seeds, 

 and die, all in the same summer. They abound in our flower 

 gardens and include most weeds. Others are biennials, 

 that is, they start from seed, develop an herbaceous shoot, 

 store food in some underground part, and die to the ground 

 in one summer ; then they use this food to form a new shoot 

 which develops seeds and dies completely the second season. 

 They are familiar in our vegetalile gardens, in Beets and 

 Carrots. Some are herbaceous perennials, that is, they 

 act like biennials except that they continue to form a food 

 supply and develop new shoots and new seeds year after 

 year. They include most of the favorites of our flower 

 gardens. Others again are woody perennials, that is, 

 they do not die back to the ground at all, unless accidentalh% 

 but persist and become woody, so that each season's new 

 growth is added upon that of the preceding year, thus de- 

 veloping shrubs and trees. Then there are some which, 

 like the annuals, flower and form seed only once in their 

 lives (monocarpic plants), Ijut take many j'ears in prepara- 

 tion. This is the case \rith the Century plant, which accumu- 

 lates food for thirty years or more, then blossoms, forms seed 

 profusely, and dies ; but the same hal^it is found in other 

 groups, including even some Palms. 



The mode of growth of the woody perennials, whereby each 

 season's growth is added upon the preceding, involves none 

 of the internal limitations of size or age to which animals are 

 subject. Hence trees continue to grow until stopped by 

 causes incident to th(>ir very size, such as the difficulty of 

 transferring a suflici<'nt wafer supply to great heights, and 

 the leverage they come to present to the action of storms, 

 whereby branches are broken, rot Fungi admitted, and decay 

 begun. Trees fortunately constructed in relation to these 



