BOTANY. 



are provided with delicate thread-like processes of protoplasm 

 called "cilia" (sing, cilium), which are in active vibration, 

 and propel the cell through the water. 



_ On placing a cell into a fluid 



A 



Ooooooo 



denser than the cell sap (e.g. a 

 ten-per-cent solution of sugar in 

 water), a portion of the water 

 will be extracted from the cell, 

 and we shall then see the proto- 

 plasm receding from the wall 

 (Fig. 4, O), showing that it is 

 normally in a state of tension 

 due to pressure from within of 

 the cell sap. The cell wall 

 shows the same thing though 

 in a less degree, owing to its 

 being much more rigid than the 

 protoplasmic lining. It is owing 

 to the partial collapsing of the 

 cells, consequent on loss of 

 ter, that plants wither W hen 



mum, showing its cellular structure. Ep., the supply of water is cut off. 

 epidermis, h, a hair, x 50. C, a cell 



from the prothallium (young plant) of a As Cells grow, new ones 

 fern, x 150. The contents of the cell con- , '. 



tracted by the action of a solution of are formed in various ways. 



If the new cells remain 



together, cell aggregates, called tissues, are produced, and of 

 these tissues are built up the various organs of the higher 

 plants. The simplest tissues are rows of cells, such as form the 

 hairs covering the surface of the organs of many flowering 

 plants (Fig. 3), and are due to a division of the cells in a 

 single direction. If the divisions take place in three planes, 

 masses of cells, such as make up the stems, etc., of the higher 

 plants, result (Fig. 4, A, B) . 



