84 COMMUNAL LIFE OF ORGANISMS SECT, n 



to their mutual advantage (Myrmecodia, Cecropia, Acacia, and Triplaris, 

 according to Belt, 1 Delpino, 2 Schimper, 3 Schumann, 4 and Warming 5 ; 

 the symbiosis of acari and plants in which the domatia (acaro-domatia) 

 are constructed for occupation by the former 6 ; the symbiosis which, 

 according to Cienkovsky, Entz, Brandt, and Geddes, prevails between 

 green or yellow algae (Zoochlorella, Zooxanthella) and animals (Radi- 

 olaria, Infusoria, Flagellata, Spongilla, and Hydra viridis), and which 

 must be regarded as mutualistic, since the alga supplies carbonaceous 

 food and oxygen, while the animal provides shelter and constantly fresh 

 supplies of water containing carbon dioxide. Reference may be made 

 here to the adaptations of insectivorous plants in accordance with their 

 peculiar method of feeding ; also to the fact that an important oecological 

 and geographical part is played by certain animals which search for and 

 utilize certain plants as food, e.g. stags, hares, mice, and the like in forest, 

 also large ruminants in savannah and desert. In this way certain species 

 of plants are favoured at the expense of others, so that the whole stamp 

 of the plant-community is changed. The manner in which plant-shape 

 may be changed by animal bites has been illustrated and explained by 

 L. Klein.' 



CHAPTER XXV. SYMBIOSIS OF PLANTS WITH ONE 

 ANOTHER. MUTUALISM 



VARIOUS kinds of bonds of very various strengths can knit plants 

 together ; in some cases the symbiosis is very intimately bound up with 

 the existence of the species concerned, in others the connexion is far 

 looser, even quite casual. 



In what follows we shall deal first with those types of symbiosis in 

 which species are most intimately and firmly linked, that is to say, 

 organically united (symbiosis, in the strict sense, oecological guilds in 

 Schimper's sense), 8 and shall gradually pass on to the looser types until 

 we conclude with the great plant-communities which include many 

 associated species, and which will be the special subject of our considera- 

 tion. The various types of symbiosis are not sharply delimited from 

 one another. 



PARASITISM. 



Parasitism is a form of symbiosis in which the two symbionts are 

 Lssociated in the most intimate manner. One species provides the other 

 witn nutriment ; the parasite lives on or in its host, and at the expense 

 of the living tissue of the host. 



/ Delpino ' see Schimper, 1898 (1903, p. 155) ; Raciborski, 1898. 



' 4 Schumann ' i888 - 1889 > i891 *' b - 



' L ^ Chiabrera, 1903. 



and arunm?* Vv^A. J H in t erde P e ndent and reciprocal relations between plants 

 madeTo C Sc^sL W-f ' ^ by Ludwig ' l8 95'. Reference should also be 



bcnimper, 1 898. 



