260 TPIE EVOLUTION THEOKY 



exhibit it still. It cannot be proved, but there seems nothing against 

 the assumption that these tangles have existed for a long time under 

 uniform conditions^ and have become adapted to these with a high 

 degree of constancy. 



The conditions are similar in the marine Alg?e of the genus 

 Caulerpa, the nearest relatives of which reproduce sexually, though 

 they themselves, as far as is known, reproduce only by spores. 



In the Lichens, which represent, as we have alread}^ seen, a life- 

 partnership between Fungi and Alg?e, amphimixis appears not to 

 occur at all ; the unicellular Alga rej^roduces by cell-division, the 

 Fungus by producing a great number of swarm-spores, which do not 

 conjugate with one another. As far as the Alga is concerned we 

 might perhaps suppose that the simplicity of its structure makes 

 it possible for it to dispense with a constant recombination of its 

 few characters to bring about the most favourable composition in 

 its idioplasm : in support of this we may note that even the life-long 

 combination with the Funo-us has caused no visible variation in the 

 Alga, as we nuist conclude from the fact that these Algae can also live 

 independently, and that the same species of Alga may combine with 

 several different Fungi to form different species of lichen, just as 

 the same Fungus may also form part of several species of lichen. 

 We might also imagine that we have here no more than a direct 

 influence of the Alga and Fungus upon one another, and that there 

 is no adaptation to the new conditions of life at all, yet that can 

 hardly be seriously maintained in regard to species which live under 

 such definite and diverse conditions. It now seems to 1)6 established 

 — contrary to the older statements — that the lichen-fungus only 

 reproduces asexually, and in face of this it seems to me that nothing 

 remains except to make the assumption that, lichens formerly 

 possessed sexual reproduction, but that they have lost it, though 

 whether all have done so is, perhaps, not yet quite certain. 



The same assumption must be made in regard to the Basidio- 

 m^Tetes among the Fungi, and for most of the Ascomycetes, for 

 in these groups of Fungi sexual reproduction has only been demon- 

 strated ' with certainty in a few genera.' That in these cases also 

 there has been a degeneration of amphigon}^ until it has completely 

 disappeared, seems probable from the two other groups of Fungi, tlie 

 Zygomycetes and Oomycetes, since in these ' a reduction of sexuality 

 amounting in some cases to complete disappearance ' can be demon- 

 strated even in existing forms. But whether it may be assumed that 

 the Fungi which are now asexual are no longer capable of new 

 adaptations, and whether their parasitic habit may be regarded 



