RELATION BETWKEX GOMDIA AND IIVI'HJ]: l.V LICHENS 179i 



observed in the form of superstructure has evidently taken place as 

 the result of the concrescence of the new thick envelopes formed 

 on the unprotected surfaces of the internal haustoria with the old 

 'envelopes of the , internal hyplue. Developing farther, the intra- 

 gonidial hyphse leave the gonidial envelopes and invade the neigh- 

 bouring gonidia. 



The processes explained above lead to a general conclusion which 

 cannot easily be reconciled with the prevailing opinion on the question 

 of the internal relations of the different components of a lichen. 

 The distinct and definite individuality of a lichen as a plant organism, 

 in view of the inexpressibility of the physiological relations between 

 fungus and alga, may readdy cause the lichen to be regarded as 

 a plant not substantially different from any othei' assimilating plant. 

 Wallroth held such a view of lichens, and Minks explained the facts 

 he had observed from the standpoint of the same theory, pushing it 

 to extremes. Elfving belongs to this grou^i. owing to his opinions on 

 the destruction of the gonidia by tlie club-shaped hyphal distentions. 

 But, since the time of Schwendener the position has not only been 

 made clear, but many times confirmed by experiment, that the lichen 

 is a two-fold organism, consisting of two components, belonging to 

 different classes of plant-systems, and all theories contradicting ,this 

 basic proposition must be regarded to-day as errors. 



Considering the lichen as an organism made up of two constituents, 

 and finding it impossible to reconcile the well-being of the whole 

 with antagonism of the constituent parts, De Bary in 1879 formu- 

 lated the theor}^ prevalent to this day, of mutual symbiosis. By 

 this the co-existence of fungus and alga in lichens was explained by 

 their mutual needs and- services resulting from their differences in 

 organisation giving rise to joint existence to the mutual benefit 

 of each, and as the final consequences the production of an organism 

 with the power of resistance of a hchen. 



The facts described above of the undoubted invasion of the 

 gonidial pi'otoplasm by the haustoria, and the destructive effect pro- 

 duced by the latter are entirely in accord with the theory of the 

 mutual assistance of the fungus and alga. As far back as 1897, 

 Schneider described and classified haustoria by means of which, in 

 his opinion, the fungus in the end absorbs the contents of the 

 gonidial cells. Somewhat later Peirce expressed an even more cate- 

 gorical conviction that the haustoria make use of the gonidial ])roto- 

 plasm, leaving the empty cell-wall. In spite of such views both the 

 above lichenologists hold the mutualistic theory. Peirce acknow- 

 ledges that he is unable to j)i'ove that the alga derives an}^ benefit 

 whatever from its co-existence with the fungus, but holds that the 

 fungus portion of every lichen is absolutely dependent upon the 

 gonidia for all its non-nitrogenovis food. It is difficult to understand 

 how the gonidia obtain nitrogen from the fungus, for Peirce himself 

 declares that the hyphte make \ise of the entire contents of the 

 gonidial cells, as we have seen from the facts described above. 



The numerous investigations of Elenkin also undoubtedly support 

 the fact of the invasion of the gonidia by the fungus hypha'. If the 

 fungus attacks its partner and feeds on its bodv, it appears decidedlv 



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