LESSON 24.] 



WOOD. 



145 



like bodies which abound on young roots are very slender projec- 

 tions of some of the superficial cells, as is seen in Fig. 337. Even 

 the fibres of wood, and what are called vessels in plants, are only 

 peculiar forms or transformations of cells. 



LESSON XXIV. 



VEGETABLE FABRIC I WOOD. 



404. CELLULAR TISSUE, such as described in the last Lesson, 

 makes up the whole structure of all very young plants, and the 

 whole of Mosses and other vegetables of the lowest grade, even 

 when full grown. But this fabric is too tender or too brittle to 

 give needful strength and toughness for plants which are to rise to 

 any considerable height and support themselves. So all such plants 

 have also in their composition more or less of 



405. Wood. This is found in all common herbs, as well as in 

 shrubs and trees ; only there is not so much of it in proportion to 

 the softer cellular tissue. It is formed very early in the growth of 

 the root, stem, and leaves ; traces of it appearing in large embryos 

 even while yet in the seed. 



406. Wood is likewise formed of cells, of cells which at first 

 are just like those that form the soft parts of plants. But early in 

 their growth, some of these lengthen and at the same time thicken 

 their walls ; these are what is called Woody Fibre or Wood- Cells ; 

 others grow to a greater size, have thin walls with various markings 

 upon them, and often run together end to end so as to form pretty 



FIG. 341. Part of a slice across the stem of the Calla -dEthiopica, magnified. 



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