198 SECTIONAL ADDRESSES. 
consist of the two elements mentioned was advanced by Schwendener 
(1867-9), who regarded the fungus as living parasitically upon the alga, 
a view which gained support from the researches of Bornet (1872), 
Voronin (1872), Treube (1873), etc., and especially of Bonnier (1886-9), 
‘ wherein synthetic cultures were obtained by bringing together (a) various 
algze obtained in the open and (b) fungus-spores isolated from cultures 
of fungi forming the one component of certain lichens. 
Schwendener’s view, that the fungi are parasitic on the alge in 
lichens, was contested by Reinke (1873) on the ground that a state of 
parasitism did not explain the long and apparently healthy life of the 
associated fungi and alge, a biological association for which the term 
Consortium was proposed by him, that of Homobiuwm by Frank (1876), 
and that of Symbiosis by de Bary (1879), the latter term denoting a con- 
dition of conjoint life that is more or less beneficial to the associated 
organisms or symbionts. 
Investigation has shown that the relation or balance between the 
associated organisms varies in different lichens. Thus in some forms 
of Collemacee, as stated by Bornet (1873), the partners as a rule inflict 
no injury upon each other, whilst in some species of Collema occasional 
parasitism of the fungus upon the alga (Nostoc) is observable, since 
short hyphal branches fix themselves to the alga cells, these swelling, 
their protoplasm becoming granular and finally being voided. In 
Synalissa and some other lichens the hypha penetrates into the interior 
of the alga, where it swells and forms a sucker, or haustorium. EJenkin 
(1902-6) and Danilov (1910) take it as proved that lichens owe their 
origin to parasitism, the fungus either preying upon the alga or living 
as an ‘ endosaprophyte ’ (Elenkin) upon the alge that die. 
Therefore, we may find in lichens the condition of true symbiosis on 
the one hand, ranging to demonstrable parasitism on the other, and, 
conversely to what has been described above, instances are known 
wherein alge are parasitic on fungi (Beijerinck, 1890). 
Physiology of Lichens. 
The nutrition of alg@ in lichens is similar to that of other chloro- 
phyllaceous plants, the most important work on the subject being that 
associated with the names of Beijerinck (1890) and Artari (1902). In 
respect to nitrogen supply, Beijerinck cultivated various green alge, 
as well as gonidia derived from Physcia parietina. The gonidia only 
multiplied rapidly in a malt-extract culture-medium to which peptones 
and sugar were added. This showed that the algze associated with 
fungi as in lichens were placed advantageously in respect to nitrogen 
supply. He termed such fungi ‘ ammonia-sugar-fungi,’ because they 
extyact nitrogen from ammonia salts and, in addition to sugar, form — 
peptones. Artari showed that there exist two physiological races in 
green alge, those which absorb and those which do not absorb peptones. 
He found that the gonidia (Cystococcus humicola) derived from Physcia 
parietina absorbed peptones, and he consequently referred to such alge 
as ‘peptone-alge.’ Treboux (1912), however, denies the existence of 
peptone-sugar-races of alge, and regards the alge in lichens as the 
Victims of parasitic fungi. Nevertheless, the important researches of 
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