62 THE TISSUES OP PLANTS 



CHAPTER m. 



ON THE TEANSFORMATION OF CELLS INTO TISSUES. 



We have already given some examples of this transfor- 

 mation of cells in plants, and have shown that it takes place 

 to a much greater extent in the animal tissues. Some 

 additional remarks are however necessary, in order to bring 

 this subject fully before the reader. 



Cellulose is at first an exceedingly tough, transparent, 

 thin, and elastic substance, which Inay be compressed or ex- 

 tended into any shape whatever. Its impassive and yield- 

 ing nature is exemplified in the innumerable varieties of 

 shape assumed by the cells. As the earthy matter is 

 deposited on the interior parietes of the cells, it gradually 

 acquires rigidity and firmness. 



Whilst in the embryonic condition, the woody and fibro- 

 vascular portions of plants are not to be distinguished from 

 the ordinary cellular tissue. The vasculares, or most 

 highly developed of the flowering plants, are at first as low 

 in organization as the cellulares or flowerless plants. This, 

 however, is with them but a transient stage of existence. 

 As soon as active life commences in the seed, the cells 

 begin to manifest their individuality, and each to perform 

 its peculiar part in the building up of the organism. Some 

 of them become rapidly elongated into fibres, others 

 coalesce into tubes, and the nutrient fluid which at first 

 equally pervaded all parts of the organism, necessarily sets 

 in a current through the vascular and fibrous tissue, owing 

 to their tubular and capillary structure. 



Now the water which enters the roots of plants from the 



