THE LTCITEN SYMBIOSIS 217 



typical chloropliyll-coiitaiiiing plants," — he does not (llscuss it further; 

 the conclusion that the "restrictive significance of the chlorophyll 

 for the whole contiguration of the vegetable world at once makes 

 itself prominent again," being really in the best style of his despised 

 Nature- Philosophers. On the other hand. West i, as a modern 

 algologist, sees clearly the deterioration of the algal constituent, 

 where this has anything that might be called a somatic factor, and 

 the de«-radation so far as this component is concerned. Hence he 

 discards the idea of ' symbiotic commensalism ' in favour of an 

 obvious condition of ' lielotism ' on the part of the alga ; the fungus 

 being clearly dominant, and the control so far unified, as in the cases 

 of the Green Hydra and the fresh- water Spongilla with intrusive 

 Chlorella, which cannot be said to present much indication of the 

 * restrictive significance ' of chlorophyll. Yet this does not touch 

 the real point at issue ; since, while the latter animals retain their 

 respective complex natural morphology entirely unaffected, the 

 Lichen -symbiosis gives what is apparently a wholly new growth-form, 

 ' previously wanting to either constituent.' Thus Schenck (in Stras- 

 buro-er's text-book) even goes so far as to state that the numerous- 

 lichenic acids are products of metabolism peculiar to the group, and 

 tliat their production is due to the "mutual chemical influence" of 

 the alga and the fungus — a wholly gratuitous conception when it is 

 remembered that chrysophanic acid (parietin), one of the best 

 known, is widely distributed, and occurs in relatively enormous 

 quantities in the rhizome etc. oiEheum. 



The attitude of Sachs is further emphasized by Goebel -, who 

 implies that the conception of a primary lichen -thallus is necessarily 

 ' dorsiventral,'' since unavoidably following the organization of a 

 * leaf -mechanism.' He further expresses the remarkable deduction 

 that all radial organization of a lichen-thallus must be hence wholly 

 secondary in origin and have been evolved from dorsi ventral struc- 

 ture in one of three different ways ; though the application of these' 

 principles to the case of the fruticose Usnea is wholly unconvincing. 

 The beautiful thallus of Cladonia verticillata (loc. cit. p. 72) is put 

 forward, from its distant resemblance (on paper) to a coticated Char a ^ 

 as illustrating how from the most different standpoints a similar- 

 morphological expression may be attained — an ingeniously perverted 

 view of homoplasy. One thus gets a general idea that in a dorsi- 

 ventral Lichen a photos^mthetic lamina acquires these properties in' 

 the same w^ay as does the dorsiventral lamina of the leaf of a higher 

 land-])lant (Sachs) — the obvious conclusion of a botanist of land- 

 flora alone, — but this onh'' begs the question ; the point still remains 

 as to how the land-plant itself ever came to attain such a space-form 

 and organization. Even the building of an elongated centric axis 

 of o-rowing hyph?e is clearly an extremely elaborate process, for which 

 one has to enquire (1) the conditions of the environment to which 

 it is the response, (2) the factors involved in working it out, 

 and (3) the mechanism by w-hich such factors may be inherited. 

 The merest w^eft of hyphal mycelium is in itself a construction of 



1 West, Algse, i. p. 37 (1916). 



2 Goebel, Organography, Engl. Trans, i.. p. 71 (1900). 



