LICHEN GONIDIA 37 



seen, he tells us, in crustaceous lichens associated with "Pleurococcus" or 

 " Cystococcus" \ they were much less frequent in the larger foliose or fruticose 

 lichens. Dead cells of Trentepohlia were also difificult to find. 



In a second paper Elenkin records one clear instance of a haustorium 

 entering an algal cell, and says he found some evidence of hyphal branches 

 penetrating otherwise uninjured gonidia, round holes being visible in their 

 outer wall, but he holds that it is the cell-wall of the alga that is mainly 

 dissolved by the ferment and then used as food by the hyphae. 



No allowance has been made by Elenkin for the normal wasting common 

 to all organic beings: the lichen fungus is continually being renewed, 

 especially in the cortical structures, and the alga must also be subject to 

 change. He^ claims, nevertheless, that his observations have proved that the 

 one .symbiont is always preying on the other, either as a parasite or as a 

 saprophyte. He has likened the conception of symbiosis to that of a balance 

 between two organisms, "a moveable equilibrium of the symbionts." If, he 

 says, we could conceive a state where the conditions of life would be equally 

 favourable for both partners there would be true mutualism, but in practice 

 one only is favoured and gains the upper hand, using its advantage to prey 

 on the other. Unless the balance is redressed, the complete destruction of 

 the weaker is certain, and is followed in time by the death of the stronger. 

 The fungus being the dominant partner, the balance, he considers, is tipped 

 in its favour. 



Elenkin's conclusions are not borne out by the long continued and healthy 

 life of the lichen. There is no record of either symbiont having succumbed 

 to the other, and the alga, when set free, is unchanged and able to resume its 

 normal development. Without the alga the fungus cannot form the ascigerous 

 fruit. Is that because as a parasite within the lichen it has degenerated past 

 recovery, or has it become so adapted to symbiosis that in saprophytic con- 

 ditions it fails to develop ? 



Another Russian lichenologist, U. N. Danilov-, records results which 

 would seem to support the theory of parasitism. He found that from the 

 clasping hyphae minute haustoria were produced, which penetrate the algal 

 cell-wall, and branch when within the outer membrane, thus forming a 

 delicate network over the plasma; secondary haustoria arising from this 

 network protrude into the interior and rob the cell-contents. He observed 

 gonidia filled with well-developed hyphae and these, after having exhausted 

 one cell, travel onwards to others. Some gonidia under the influence of the 

 fungus had become deformed and were finally killed. As a proof of this 

 latter statement he adduces the presence in the thallus of some gonidia 

 containing shrivelled protoplasm, of others entirely empty. He considers, as 

 further evidence in favour of parasitism, the finding of empty membranes as 



' Elenkin 1906-. * Danilov 1910. 



