1 903 Symbiosis 1 5 7 



a similar class associating together, — or again, different 

 species in the vegetable world combining together for 

 some mutual advantage. 



Ecology treats of plants in the broadest sense of this 

 benefit association, such as the gathering and living together 

 of plants inhabiting the same element or position — accord- 

 ing to moisture, heat, cold, cS:c. — necessary for their well- 

 being, as hydrophytes or lithophytes. But the more 

 intimate relations of individuals may more properly be 

 termed Symbiosis. 



Referring to the large subject of the advantages which 

 animals and plants share with one another, it is only 

 necessary to quote two instances : that of many flowering- 

 plants which secrete honey, and attract insects of many 

 kinds, who, in return for the nectar, unconsciously distribute 

 pollen from one flower to another, rendering the production 

 of fertile seeds possible. Or another, perhaps less commonly 

 known instance, that of certain marine green algse which 

 inhabit sea-anemones ; the green parts of the alga having 

 the property of breaking up carbonic acid gas and liberating 

 the oxygen which is necessary to the breathing operations 

 of the animal. On the other hand, the plant absorbs the 

 carbonic acid breathed out by the animal, illustrating the 

 ancient saying that "a good exchange is no robbery." 



Phanerogams, or flowering -plants, may be associated 

 with other flowering-plants, or with cryptogams, in much 

 the same way ; also cryptogams with lower orders of 

 vegetation, those which reproduce their kind by spores and 

 not seeds, or by the simpler methods of buds breaking off 

 from the original plant and producing new ones. 



In all cases of symbiosis among plants, be it noticed, 

 there is on one side a plant containing an abundance of 

 chlorophyll, and on the other an organism which has none 

 or a very small quantity. The obtaining of a food-supply 

 is the chief reason for these co - operative associations. 

 Chlorophyll, as every one knows, is the green colouring 

 matter distributed in the body of the plant in minute 

 corpuscles called chloroplasts. Chlorophyll is only de- 

 veloped in these chloroplasts in parts of the plant exposed 

 to light. Their use is to help in the process of the 



