392 BOTANY. 



dons are greatly thickened, the latter remain for some time 

 inside of the seed ; in other cases, however, they soon with- 

 draw themselves, and become expanded as the first leaves 

 of the plantlet. The young plant is quite simple at first, 

 but, with the development of each succeeding internode, it 

 becomes more like the adult plant. 



502. — The three tissue systems are generally well de- 

 veloped in Phanerogamia. The epidermis is copiously sup- 

 plied with stomata, and itself consists of one or (rarely) more 

 layers of cells, whose external walls are generally somewhat 

 thickened, and whose cell contents rarely contain chloro- 

 phyll. Trichomes of various forms are abundantly de- 

 veloped. The fibro-vascular bundles are of the form called 

 by De Bary collateral bundles, the only exception being the 

 first formed one in the root, which is of the radial type. 

 The bundles are symmetrically arranged in the stem, through 

 which they pass vertically parallel to each other. They are 

 mostly common — i.e., they extend from the leaves into the 

 stem ; but some are strictly cauline — i.e., they are found 

 only in the stems and have no connection with the leaves. 

 All the kinds of tissues, with the exception of collenchyma, 

 may occur in the bundles ; but they are mainly made up of 

 tracheary, sieve, and fibrous tissues. In the larger perennials, 

 as the trees, the great mass of tissue in the woody stems is 

 principally made up of the tracheary and fibrous tissues of 

 the fibro-vascular bundles. In succulent plants, especially 

 those growing in water, the bundles are usually smaller and 

 more simple, being sometimes reduced to a thread of trache- 

 ary or sieve tissue. 



In the fundamental tissues parenchyma, in its various 

 forms, is by far the most common. The hypodermal por- 

 tions are frequently composed of collenchyma or scleren- 

 chyma. Laticiferous tissue is common in the fundamental 

 system of certain orders. 



503. — By far the greater number of Phanerogams are 

 chlorophyll-bearing plants, comparatively few only being 



books, said to be albuminous, while those in which it is wanting are 

 said to be exalbuminous. 



