69 



re-acted or responded in a particular way, the final result of 

 such response being manifested in the obvious movements of 

 the leaf and leaflets. 



63. The protoplasm in the The Cell. 



majority of plants does not occur in naked masses but sur- 

 rounds itself with an elastic, membranous wall, of a substance 

 called cellulose, inside of which it lives. Such an enclosed 

 piece of protoplasm is called a cell and its outer envelope the 

 cell-waU. Many plants are known, each of which consists of 



only a single cell, but the body of the more highly organised 

 plants with which we are chiefly concerned is made up of a 

 multitude of such cells which live together in intimate contact, 

 although every such plant originally began life as a single 

 minute cell. 



64. If a thin section from the Ceil 



growing apex of such a plant is examined with a microscope, it Contents. 

 will be found to consist of a number of nearly cubical cells, 



each of them being provided with a delicate cell-wall and all of 

 them fitting closely together. Each cell is full of protoplasm 

 and contains in the centre a rounded body called the nucleus 

 which is separated by a definite boundary from the rest of 

 the protoplasm. If the protoplasm is treated with a suitable 

 stain, the nucleus is seen to consist of a number of fine 

 twisted threads, or filaments, which become more deeply 

 coloured than the rest of the protoplasm. The latter, which 

 fills all the rest of the cell outside the nucleus and which 

 usually contains distinct granules, is distinguished as cytoplasm. 

 As such a cell increases in size the protoplasm is no longer 

 able to completely fill its cavity and spaces, the so-called 

 vacuoles, arise in the protoplasm which usually occupy the 

 greater part of the mature cell, the protoplasm being confined 

 to a layer around the cell-wall, with perhaps a few connecting 

 threads across the cell cavity. However large the vacuoles 

 may be, there is always a continuous layer of cytoplasm 

 surrounding the nucleus and lining the inside of the cell- wall. 

 The vacuoles contain a watery fluid termed cell-sap which con- 

 tains a variety of substances in solution, some intended as food 

 for the protoplasm and others having been excreted by the 

 protoplasm as waste products. The cell-sap also frequently 

 contains a red, or blue, colouring matter called antliocyanin, 

 to which the colour of many flowers, fruits and young leaves 

 is due. The cytoplasm in such a cell is often seen to be in active 

 movement, the latter being indicated by the granules contained 

 in it, which are seen to be carried along by the living pro- 



