42 THE JOURNAL OF BOTANY 



morphological differentiation of centric or dorsiventra] axes, and 

 ramuli of different degree, is hut the vestigia of an algal soma, 

 adapted to the normal factors of marine biology, and following its 

 seaweed phylogeny in the recapitulatory production of reproductive 



organs as ' trichome-derivatives,' whether in the form of a confluent 

 4 hymenium ' (Laminaria ; apothecia), or even as immersed and 

 perithecium-like conceptacles ( Funis and Floridean cystocarps). 

 Incidentally it now becomes clear why higher Fungi repeat the com- 

 plex life-cycle and phases of sexual and asexual reproduction charac- 

 teristic of the higher algal types of the modern sea (cf. Florideaj). 

 There can be no doubt that the heterotrophic Fungus-soma continues 

 the heterotrophic region of the older algal somata, without being in 

 any way a production de novo, designed to meet the special conditions 

 of a saprophytic existence ; just as in an older Plankton-phase the 

 heterotrophic ' animal ' arose by continuing the holozoic method of 

 nutrition common to all naked flagellate life, but merely eliminated 

 the autotrophic chloroplasts, or only their autotrophic function, since 

 vestiges were retained as ' eyes ' sensitive to the same octave of solar 

 radiation. 



Beyond such a stage of continued rather than incipient hetero- 

 trophy, the Lichen covers a special biological case, also readily in- 

 telligible to those who have seen the films and scums of low-grade 

 green flagellate and coccoid forms which accumulate in any vessel 

 of standing sea-water exposed to the light. While the main series of 

 higher Eumycetes are clearly derivative from stripped seaweeds 

 which emerged from the water to continue existence at the expense of 

 stored carbohydrate of decaying land- vegetation, the Lichen repre- 

 sents the case of similar simple or branched algal somata, remaining 

 denuded of autotrophic tissue in standing pools, and hence soon 

 smothered with a growth of green autotrophic flagellates, now ready 

 to take advantage of the penetrable tissues of the enfeebled hosts, in 

 their demand for a benthic substratum. The heterotrophic hosts. 

 enclosed in a new mantle of photosynthetic units, merely require to 

 continue their heterotrophic metabolism at the expense of the waste 

 carbohydrate and photosynthetic oxygen, in such a medium only 

 available in the vicinity of these autotrophic units. The synthesis 

 is thus effected in terms of (1) a substratum for the flagellate on 

 attaining the benthic habit, and (2) the only possible means of con- 

 tinued life in the light, or even in the dark, for the more massive 

 Fungus-' host.' The former point is of interest, since in the con- 

 sideration of any possible advantage to the algal constituent of the 

 Lichen, shelter is commonly postulated, or protection from desiccation ; 

 the older vital problem of the struggle for substratum heing naturally 

 lost sight of in the consideration of subaerial migrants. It is in- 

 teresting to note, again, that such a hypothesis precludes the possi- 

 bilitv of the recovery of a cortical system by the host, which might 

 be expected to follow in such a case as that of Fucus, in which 

 an apical cell, though itself largely heterotrophic, might conceivably 

 survive to regenerate a new somatic region by an apical meristeru. 

 But apical lneristems are only presented in special types among algae ; 

 the primary case being a condition ol general intercalary growth ami 



