THE 



STRUCTURE AND RE- 

 PRODUCTION OF PLANTS 



PART I 

 THE ANATOMY OF PLANTS 



CHAPTER I 

 THE STRUCTURE AND PHYSIOLOGY OF THE PLANT-CELL 



EVERY living organism, whether animal or plant, is composed 

 of one or more minute units called cells, and this applies even 

 to those forms of life which are so small that they can only be 

 seen with the help of a microscope. The green powdery cover- 

 ing so often present on tree-trunks and palings consists of multi- 

 tudes of single-celled plants (Pleurococcus, Fig. 102, p. 192), whilst 

 millions of cells together form the body of a garden weed or 

 tree. Organisms of the latter type are described as multicellular , 

 whilst those consisting of a single cell are termed unicellular. 



The structure of a cell will best be realised if a typical example 

 is studied, such as that obtained by stripping off the skin (or 

 epidermis) from the inner surface of an Onion-scale. If a small 

 portion of this be mounted in water, and examined under the 

 low power of a microscope (see Appendix I), it will be seen to 

 consist of a large number of oblong cells connected together 

 without any intervening spaces to form a tissue (Fig. I, A). 

 The network of delicate lines separating the individual units 

 is constituted by the cell-walls, which are all joined to one another. 

 In each cell a colourless, somewhat dense granular substance 

 (the cytoplasm, Fig. i, B, Cy.) is visible, particularly around the 

 i 



