TISSUES 



Hi 



Fig. 52. — I, Young cell previous to cell-division ; 

 2, the same after division of the nucleus ; 3, cell- 

 division completed (enlarged 500 diameters). 



right angles to a straight line drawn from one nucleus to the 

 other (Fig. 52). 



From ordinary examination of cells and their contents, it 

 might be concluded that 

 the living materialof a typi- 

 cal plant-cell is completely 

 shut off by the cell-wall 

 from communication with 

 its immediate neighbours. 



Comparatively recent re- 

 search has, however, shown 

 that in a number of in- 

 stances, the protoplasm of 

 one cell is connected with that of adjoining cells, by means of 

 extremely delicate protoplasmic strands which pass through 

 minute openings in the cell-walls, and it appears very probable 

 that the whole protoplasm of an organism is continuous. 



In some instances, as in the embryo-sac of the ovule, the suc- 

 cessive division of a nucleus and its associated cytoplasm goes on 

 for a time without being immediately followed by the formation of 

 corresponding cell-walls ; sooner or later, however, the protoplasm 

 of almost all vegetable cells becomes enclosed in a cell-wall. 



6. Tissues. — The body of a plant consists of a vast number of 

 cells of very varied forms. These different kinds of cells, instead 

 of being distributed uniformly through the plant, are associated 

 together in the form of bands, plates and cylindrical masses : 

 such associated groups of cells are spoken of as tissues. The 

 latter may be classified in many ways according as we take into 

 consideration their origin, structure or function. A tissue con- 

 sisting of thin- walled living cells which are embryonic and capable 

 of division is termed a meristem or formative tissue, the fuUy^ 

 developed adult tissues being spoken of as pirinanent. 



Taking into consideration the form of the cells composing 

 them, two chief types of tissues may be distinguished, namely, 



