236 THE INFLUENCE OF LIGHT ON LIFE. 



bottom part of the plant's stem is protected from the light, and is 

 thereby rendered more succulent and desirable as an article of 

 food. 



Different species of plants require different amounts of light. 

 Some are very greedy and some are content with a very little 

 indeed. In the deepest parts of the sea, where perpetual darkness 

 reigns, we are told that there are no plants at all ; but in shallower 

 waters where there is a certain degree of light, although the quan- 

 tity may be very small, seaweeds are to be found in abundance. 

 In Messrs. Kerner and Oliver's book on The Natural History of 

 Plants^ a certain moss (Hookeria splendens) is referred to, which 

 lives chiefly in hollow tree-trunks. The light in such situations is 

 necessarily often very feeble, yet this moss is noticeable for its 

 glossy green. On examination the leaves are found to be very thin 

 and delicate, but the cells of the leaves which are turned to receive 

 the scanty light are convex and act somewhat like lenses, and 

 condense the light on to the granules of chlorophyll which He 

 behind these convex cells. By such a beautiful contrivance as 

 this are these humble plants able to concentrate sufficient light 

 to enable them to secure for themselves the carbon which they 

 require. 



We all know that in shady nooks and sheltered corners quite 

 different species of plants may be found from those which may be 

 found in exposed places and in the full blaze of sunlight. No one, 

 for instance, would ever think of looking for a rose in the darkest 

 parts of the woods, nor would we think of looking for the health- 

 iest ferns or mosses in such places as would be most congenial to 

 the rose. We may find fungi in dark — indeed, altogether dark — 

 places; but then we know that fungi are different from other plants, 

 as they do not produce chlorophyll, they being producers of car- 

 bonic acid instead of decomposers of it. 



We have now seen that the presence of a moderate supply of 

 light has an influence in sustaining the life of certain plants, and 

 even in bringing about a luxuriance such as we often see in grottoes 

 of ferns ; we have seen that even a very little supply of light indeed 

 has an influence in sustaining such plants as possess the power of 

 gathering up the scanty rays ; and we have also seen that when the 

 supply /^//j altogether^ then life ceases. 



