334 PLANT LIFE. 



20.) In a somewhat similar way certain bacteria are found 

 always massed into colonies, constituting a sort of thallus of 



a 



FIG. 371. A, serpent-like colonies of Chondromyces serpens, composed of numerous 

 rod-shaped individuals, B, a, which multiply by fission, b, and secrete a mass of jelly 

 which holds them together. A magnified 45 diam.; B, 750 diam. After Thaxter. 



characteristic outline (fig. 371). In the higher fungi, also, 

 the mycelium may be looked upon as a thallus formed by the 

 aggregation of many individuals ; for, while it is possible to 

 have a mycelium produced from the development of a single 

 spore, it is not common. The mycelium is generally the 

 result of the union of hyphse (see ^[ 50) arising from many 

 spores. Even in such cases the mycelium may constitute 

 a single body, and may give rise to a single fructification. 



457. 2. Between plants of different species. - -Mutual- 

 ism is more common between plants of different species. It 

 takes the following forms: 



458. (a) Lodgers.- The higher plants often shelter 

 various species of lower ones within their intercellular cham- 

 bers, or in pockets formed by lobes or bladders of various 

 sorts. This relation is especially common between water 

 plants and algae. Species of Nostoc live in the intercellular 

 spaces of liverworts and duck-weeds, in the cortex of the 

 roots of some land plants, and in the bladdery leaf-lobes of 

 liverworts. Some species of the higher algae, also, are 

 frequently associated with other species to which they attach 

 themselves. That they are not merely epiphytic (see ^[ 454) 

 is shown by the fact that certain species are found only upon 

 certain other species, while they do not grow upon other 



