SYMBIOSIS IN FEBN PROTHALLIA 



PROFESSOR DOUGLAS HOUGHTON CAMPBELL 

 Stanford University 



The symbiotic associations so frequently met with in 

 plants present one of the most interesting phenomena 

 with which the biologist has to deal. While these asso- 

 ciations are often not easily distinguishable from true 

 parasitism, in many instances there is a genuine symbi- 

 otic relation and, although there may be a certain degree 

 of parasitism, there is no question that these associations 

 are for the most part beneficial to both of the forms con- 

 cerned. Indeed, the very existence of one or both of the 

 symbionts may depend upon it. 



In most cases of symbiosis, one of the symbionts is a 

 fungus, but this is not always so. Certain of the Schizo- 

 phyceae or blue green algoa are very commonly associated 

 with higher plants in what appears to be a symbiotic re- 

 lation, although the nature of the association in this case 

 is still very obscure. The Anthocerotacere and several 

 of the liverworts, like Blasia, always have within their 

 tissues colonies of a Nostoc, and the little water fern 

 Azolla invariably harbors in each leaf a colony of the 

 Nostoc-like Anabana AzoUa. Nostoc has been found to 

 occur in the roots of Ci/cas reroluta and Gunnera among 

 the seed plants, and the Schizophycea? also frequently 

 constitute the "gonidia" of many lichens. The associa- 

 tion of the nitrogen-fixing bacteria with the root nodules 

 of the Leguminosae is also a well-known case of symbiosis. 

 Of the true alga* there are a number of species recorded, 

 e. g., Chlorochytrium Lemme, which live within the tis- 

 sues of higher plants, but it is doubtful whether the host 

 is in any way affected by the presence of the alga, which 



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