98 ELEMENTS OF STRUCTURAL BOTANY. 



being either pale or brownish. The Mistletoe, however, 

 is a green parasite. 



136. As to duration, roots (and, consequently, the 

 plants themselves) are either annual, or biennial, or 

 perennial. The plant is called an annual if its whole life, 

 from the germination of the seed, is limited to one 

 season. It is biennial if it flowers and ripens its seed 

 in the second season. Between these two classes it is 

 difficult to draw a sharp line, because, with proper care, 

 some annuals may be induced to live for two years; and, 

 on the other hand, some plants, as the Radish, which ' 

 are properly biennial if the seed is sown in the fall, will 

 flower and produce seed in one season if sown in the 

 spring. Something, also, depends upon the climate in 

 which the plant is grown, its life, in some cases, being 

 prolonged in a more favourable situation. Perennials 

 live on year after year, as is the case with all our shrubs 

 and trees, and also with some herbaceous plants, as Peony 

 and Dahlia, which only die down to the surface' of the 

 ground in the autumn. 



137. The Stem. As the root is developed from the 

 lower#end of the radicle of the embryo, so the stem is 

 developed from the upper end, but with this important 

 difference, that a hud always precedes the formation of 

 the stem or any part of it or its branches. If a bud, sUch 

 as that of the Lilac, be picked to pieces, it will be found 

 to consist mostly of minute leaves closely packed together 

 on a short bit of stem. A bud, in fact, is only a special 

 condition of the extremity of the stem, and is not to be 

 regarded as an organ distinct from it. As the bud unfolds, 

 the stem may lengthen so as to exhibit the internodes, or 



