218 THE JOUR]SrAL OF BOTANY 



iiulefinite complexity (as also antiquity) ; once it is grasped that the 

 ordinary filamentous mycelium of a heterotrophic Fung-us can be 

 onl}^ attained via a period of autotrophic filamentous and probably 

 massive marine phj^tobenthon, itself in turn the highly elaborated 

 adaptation of a plankton life-history. The idea begins to emerge that 

 the ^physiological resemblance in functional organization between a 

 liehen-thallus and a leaf-lamina represents a phenomenon of conver- 

 gence in widely divergent series of the plant-kingdom, which only 

 meet in their common ancestry in the sea ; and the point arises as to 

 what factors they ma}'^ have had in common at that epoch. Sachs as 

 the typical land-botanist takes the land-plant for granted, as if one 

 could not possibly make an autotrophic organism of the land in any 

 other way. 



On the other hand, after eliminating all that can be said with 

 regard to (1) the Holo parasitism of the Fungus; (2) the Helotism 

 of the alga in the protective and secluded recesses of the fungus- 

 mycelium ; (3) the direct analog}^ of such a 'dual' organism to the 

 })henomena of ' intrusion ' presented by the case of the Grreen Hydra, 

 the Uadiolarian with its Zooxanthellai, or the green fresh- water 

 sponge ( Spoil f/ ilia), as also the story of the decadence of the green 

 marine worm, Coniwlufa, there yet remains a residual factor, which 

 is the one covered b}'^ the term ' consortium,' as the undoubted fact 

 that the mycelium of the Fungus concerned, beginning ontogeneti- 

 cally as a structureless weft, does produce a soma with distinctive 

 form-factors, readily identified b}^ collectors, hi terms of thalloid 

 shoots of differentiated appearance, symmetry, texture, and ramifica- 

 cation, wliicli constitute the ' Li chen- Plant,'' as a distinct type of 

 vegetation demanding analysis and explanation. It is in such definite 

 form-factors that the special interest of the group now centres. In 

 other words, the discussion of the Lichen resolves itself into : (1) the 

 story of the dominant Fungus; (2) the story of the Alga in a 

 condition of 'beneficent slavery' ; (3) the story of something which 

 is possibl}^ neither, but apparently new, and commonly accepted as a 

 ' consequence of the symbiosis.' 



One looks in vain among the writings of Lichenologists for any 

 adequate appreciation, analysis, or even in most cases intelligible 

 description of the form-factors of a Lichen; and yet it should be 

 sufficiently clear that if these have arisen de novo, since the subaerial 

 s^anbiosis began, they must have a most significant bearing on the 

 manner in which physiologically specialized somata may be put 

 together. Each individual factor requires to be isolated, scheduled, 

 and accounted for at its exact biological vahie, as solving some parti- 

 cular and insistent problem of the two symbionts, which should be 

 within recall. All Lichens are admittedly vegetation of the land, and 

 adapted to one general set of subaerial conditions, involving moisture, 

 free oxygen, and light-supply, with some source of food-salts. No 

 more delightful study could be offered a Lichenologist than the 

 building-up of the history of the progressive attainment of a wholly 

 new somatic organization, step by step, from the earliest syntheses. 

 The details of some such syntheses, with very beautiful figm-es, are given 

 by Bonnier (1889) for Fhi/sda, but they stop just as they begin to 



