204 ELEMENTS OF SCIENCE 



of differently shaped cells aggregated in masses so as to 

 appear as bands of different colours when it is cut 

 transversely. These bands consist of fibres and tubes 

 amidst large polygonal cells containing many granules 

 of starch which is a non-nitrogenous substance that 

 plants produce abundantly. 



The fronds are green, flattened and much sub-divided 

 expansions, invested on their upper surface with a layer 

 of irregularly shaped cells forming what is called the 

 epidermis. Beneath this is a mass of cells containing 

 chlorophyll, which gives its green colour to the frond. 

 The under surface of the frond is coated with cells and 

 hair-like processes, while between many of the cells 

 are small openings, termed stomata, which allow air to 

 enter and penetrate the cavities (left between the cells 

 which form the substance of the frond), termed inter - 



Thus the important process of dissolving carbonic acid 

 and fixing its carbon while its oxygen is set free, takes 

 place in the interior of the plant, as well as does the 

 process of respiration. 



If a frond be cut during summer, another will soon 

 grow up, and takes its place. Thus we have a process 

 of reparative growth, much more complex and complete 

 than is the reparation of a mutilated crystal, or plant- 

 like aggregations of crystals, which is the nearest 

 approximation to true " growth " that is to be met 

 with in the non-living world. In the fern, however, we 

 have a mode of growth to which nothing in the non-living 

 world makes even the faintest approximation. 



Under the margin of a full-grown frond will be found 

 a groove containing a series of small brown bodies, each 

 of which is called a sporangium, because it is a little 

 membranous bag that contains spores, which bag bursts 



