RECENT OBSERVATIONS ON THIS GONIDIA QUESTION. 121 



algal-types " of the " lichen-gonidia." ^ He points out that 

 there is a large number of lichens in which the gonidia con- 

 stantly belong to the same type, this indeed being the preva- 

 lent case, Avhilst there are other lichen forms which evince a 

 certain amount of oscillation in their selection of gonidia 

 between related algal-forms. These he briefly discusses, con- 

 cluding by a reference to the question of "parasitic algse." 

 He admits that the parasitism which, in conformity with his 

 theory, must be assumed for the lichens, would remain 

 unique in the vegetable kingdom. However, certain 

 recent observations bring to notice cases of adaptation in 

 a certain sense analogous. He especially quotes the occur- 

 rence of iVbs^oc-chaplets in the substance of Azolla recorded 

 by Strasburger, who found these algse in the leaves of every 

 species of Azolla which he had examined, no matter from 

 what quarter of the world they originated, which fact 

 almost led him to suppose that this plant could not have 

 been altogether passively related to algae. "One might 

 almost believe " (says Strasburger) " that the iVo^/oc-chaplets 

 are useful to the leaves of the Azolla in their Avork of assi- 

 milation, and thus, in a certain manner, play a similar part 

 in them as in the interior of the lichen- thallus." Schwen- 

 dener then alludes to E-einke's observation of a Scyto- 

 nematous plant in the interior of Gunner a [loc. cit,~), also 

 to those of Cohn {loc. cit.^), and proceeds to remark that in 

 what the dependence consists — especially as regards the pro- 

 cesses of nutrition — is at present unknown, but that it cannot 

 be assumed from Cohn's case that the relation is a reciprocal 

 one. The questionable "parasitic" algee accordingly, he 

 holds, stand in decided ojiposition to the gonidia-formers ; 

 in how far, indeed, they are true parasites appears to him in 

 the meantime still doubtful. However it may be, such 

 phenomena, he holds, abundantly show that the conditions of 

 dependence in which organisms may stand to one another 

 are bound up in no particular law, but rather may make 

 themselves evident as the expression of mutual adaptation in 

 the most diverse modes. And thus, he urges, his doctrine of 

 the algal nature of lichen-gonidia may contribute to place in 

 a correct light a series of the most noteworthy adaptations 

 which occur in the vegetable kingdom. 



1 Cohn : ' Beitriige zur Biologie der Pflanzen,' Heft IT, p. 87. See also 

 ' Quart. Journ. Micr. Sc.,' vol. xiii, n. s., p. 366. 



2 " Die Algentypeu der Flechtengonidien," Basel, 1869. See ' Quart. 

 Journ. ]Mic. Sc.,' vol. xiii, n. s., pp. 222 et seq. 



3 Reinke : ' Bot. Zeitung,' 1872, p. 59. 



