178 M. C. COOKE ON THE DUAL-LICHEN HYPOTHESIS. 



takes place. That the most vigorous functions of life are carried on 

 in their proximity. 



As the Schwendenerian theory is wholly based on the belief that 

 there is no genetic relationship between the hypha3 and the gonidia 

 of the Lichen thallus, any proof that such a genetic relationship does 

 exist is fatal to it. Dr. Minks, of Stettin, has directed his attention 

 specially to the investigation of this point with very important 

 results. He discovers in the hyphaa of Lichens two new organs, 

 which he has designated geonangium and gonocystiam, which produce 

 gonidia within the walls of the hyphaa themselves. These gonidia, 

 because of their minuteness, he names micro-gonidia. He has seen 

 these micro-gonidia in all the cells of the hyphas, whether in the 

 vegetative or the reproductive parts. He sees them in the cortical 

 layer, the medullary layer, the paraphyses, the young asci, the 

 sporidia, &c. Thus he has established their existence, not only 

 within the hyphae-cells of all parts of the Lichen, but also in all 

 stages of its life-history.* 



These facts, so utterly subversive of the Schwendener theory, have 

 likewise been observed and confirmed by Dr. Miiller, of Geneva, who 

 says, " My results have surpassed my highest expectations. Not 

 only have I proved the existence of micro-gonidia in all the organs 

 mentioned above, after having treated them with caustic potash, sul- 

 phuric acid, and tincture of iodine, but I have also seen them with 

 my excellent immersion objectives, without any chemical prepara- 

 tion ; and in favourable cases, I have even seen them with the non- 

 immersion lower powers of Hartnack." He proceeds to say that 

 these micro-gonidia are paler than the ordinary gonidia, and dis- 

 posed in moniliform series in the axes of the hyphas, having a 

 diameter of '001 mm. In certain tropical species, which had been 

 exposed to a more vivid light than those in more northern lati- 

 tudes, these micro-gonidia attained a brighter green ; for example, 

 in Parmelia prolixa, var. erythrocardia, Miill., sent by Dr. 

 Schweinfurth from Lake Nyanza, in Africa. In this Lichen they 

 were so green that little difference of colour existed between them 

 and the gonidia. j" 



If the " parasite " can produce within itself all which it requires 



* Since the above was written some Lichenologists have rejected the con- 

 clusions deduced from Dr. Minks' experiments. Whilst contending that 

 gonidia are organs pertaining to the Lichen, they consider them independent 

 of the so-called Micro-gonidia. 



f Consult Minks on Micro-gonidia, in the " Eegensburg Flora," for 1878. 



