278 STRUCTURAL BOTANY 



scribed under the name of B. radicicola. Eecent in- 

 vestigations appear to show that the organism is really 

 one of the Bacteria. In any case the relation of 

 this creature to its leguminous host seems to be one 

 of symbiosis, or mutual service, rather than of one- 

 sided parasitism. 



TYPE XXV. ClADOTHRIX DICHOTOMA 



We have chosen this plant as an example of another 

 group of so-called Bacteria, which probably, however, 

 have little to do with the true Bacilli and their allies. 

 Cladothrix dichotoma is a very common organism in 

 impure water. A very moderate degree of impurity is 

 sufficient to provide it with food, for it sometimes 

 appears in vast quantities in the pipes of an ordinary 

 water-supply, where it forms dirty-white masses, which 

 may even choke up the taps. 



In its vegetative condition the plant forms long 

 branched threads, attached at one end to some solid 

 substance. The filaments are composed of a single series 

 of rod-shaped cells (Fig. Ill), and are enclosed in a 

 gelatinous sheath. The branching is not genuine, for it 

 does not depend on the formation of lateral outgrowths, 

 or on a true dichotomy of the growing-point. The 

 gelatinous sheath offers a certain resistance to the growth 

 of the filament within, which consequently breaks across, 

 and the two parts grow past each other at the point of 

 rupture. Exactly the same kind of apparent branching 

 occurs in some of the blue-green Algre, which Cladothrix 

 and its allies closely resemble. The contents of the 



