296 



PLANT STUDIES 



Tf ;i Lichen be sectioned, the rehition between the syni- 

 bioiits will be seen (Fig. 273). The tnngns nuikes the bnlk 

 of the body with its interwoven mycelial threads, in the 

 meshes of which lie the Alga?, sometimes scattered, some- 





''ii;.^;7^. Section ttirnu^'h thallns of a lichen (S/ir/a). sliowin;; holdfasts (/■), lower (ti) 

 and upper io) surfaces, fungus hyphte {in), and enmeshed algie {g). — After Sachs. 



times massed. It is these enmeshed Alga% .showing throngh 

 the transparent mycelinm, that give the greenish tint to 

 the Lichen. 



Li the case of Lichens the symbionts are tliought by 

 some to be mntnally helpfnl, the alga mannfactnring fodd 

 for the fungus, and the fungus providing protection and 

 water containing food materials for the alga. Others do not 

 recognize any special benefit to the alga., and see in a Lichen 

 simply a parasitic fungus living on the products of an alga. 

 In any event the Algie are not destroyed but seem to thrive. 

 It is discovered that the alga symbiont can live quite inde- 



