20 ELEMENTARY ORGANS OF PLANTS. 



contiguous cells are wholly absorbed in the process of growth, 

 and woody fibre and vascular tissue enter into composition. 

 It will be easy to perceive, from these facts, how, from so sim- 

 ple an element as a cell, may proceed a countless number of 

 different forms of tissue. 



9. The substance out of which the cells of plants are formed 

 is called Cellulose, which is of universal occurrence in all 

 plants. This cellulose is formed out of a viscid mucilaginous 

 fluid termed by vegetable physiologists cambium, or organiz- 

 able matter, which fluid always precedes the appearance of 

 the cells, and is ever present when vegetable matter is in a 

 state of growth. 



10. A stratum of cambium appears in the young and vitally 

 active tissues of plants in the spring of the year, and renders 

 the bark so easily separable from the stem of plants at this 

 season ; this fluid matter is gradually organized into cells, and 

 by the addition of these to their previously developed tissue, 

 the growth of the plant is effected. In autumn, this cambium, 

 or fluid matter, gradually disappears, the cells cease to form, 

 and the parts of plants to elongate and enlarge, and the bark 

 and stem again become firmly adherent. 



11. True cellulose is always excessively thin and plastic 

 when first developed, so as to be easily impressible into any 

 form whatever. To this first layer of cellulose the well-contrived 

 term Protoplasm (-tguto; first, and rtxaa^ua formative matter), 

 first proposed by Professor Mohl, is now applied. The thick- 

 ness and rigidity afterwards acquired by cellulose are owing 

 to the internal deposition of layers of incrusting matter which 



