

FUNGOUS ROOT-TUBERCLES. 63 



fungu 



the 



be found as in Ceanothus. When mature, the fungus forms 

 a dense cluster in the infected cells, the central portion of 

 which is composed of completely branched threads bearing 

 spherical sporangia at their end. Atkinson considers this 

 fungus as a distinct species from all other forms, and pro- 

 poses the name Franlcia ceanothi. A symbiotic relationship 

 between the host and parasite seems probable to Atkinson 

 from the fact that the plant appears to suffer in no respect 



from the infection. 



It was left for Hiltner (16) to prove experimentally that 

 the root tubercles on the alder enable the plant to assimilate 

 the free nitrogen of the air by a process analogous to that 

 which occurs in leguminous plants. Furthermore he showed 

 that alder plants can grow without tubercles provided the so- 

 lution or soil in which they grow contains nitrogen in some 

 form, and conversely that the growth of the tubercles is in- 

 hibited when the plants are grown in a solution or soil where 

 nitrogen is present in abundance. Calcium nitrate entirely 

 stopped the growth of the tubercles. 



Subsequent to the above investigation, the attention of 

 Nobbe and Hiltner (28) was called to Podocarpus, an ori- 

 ental conifer, which possesses a large number of root-tubercles 

 caused by an endotrophic mycorrhiza. Guided by their ex- 

 periment on the alder they carried on investigations with 

 greenhouse plants grown in quartz sand to which only non- 

 nitrogenous culture solutions were added. For five years be- 

 fore their results were published the plants grew luxuriantly 

 and they concluded that they obtained the required nitrogen 



from the air. 



Although Schacht (32), Brunchorst, Moller and a few 

 other earlier investigators had examined the root-tubercle- 



f 



species grown in green-houses, it was not until 1901 that Life 



more 



that a fungus, a bacterium, and an alga inhabit these struc- 

 tures. In young tubercles and in the tips of older ones, he 



found only the fungus and bacteria, which, he claims, pre- 



