THE LICHEN AS TRANSMIGRANT 43 



extension throughout the whole mass, or over localized areas [cf. 

 Enteromorpha (Chlorophyceaj), Asperococcus (Phaeophycese); Dilsea, 

 Khodi/menia, Gigartina (Floridese)]. From this it may he said to 

 follow that no Lichen is likely to have an apical meristem in the 

 sense of a segmenting apical cell ; and as a matter of fact the 

 Lichen-habit is largely confined to algal types of the lowest grade, in 

 which intercalary growth and ramification of the most generalized 

 character still obtain (cf. Mesogloia and Helminfhora-type with 

 JJsnea and Gladonia). The more elaborate somata of the Lichen - 

 series attain a phase with apical growth in the ultimate ramuli of 

 the type of such Floridese as Polg ides and Eurcellaria, Chondrus 

 and Gigartina, in which the general presentation of Lichen-form is 

 sufficiently striking in the living condition, to be even more empha- 

 sized when subjected to desiccation on drying in the manner of 

 modern subaerial lichens. 



Such a working-hypothesis covers much of the fundamental 

 organization of a Lichen-fungus. One now begins to obtain a clear idea, 

 not only of the locus of its transition to the heterotrophic condition, in 

 common with associated saprophytic Ascomycete phyla, but of the 

 mechanism of the original failure of the photosynthetic tissue, primarily 

 due to the lack of oxygen for respiration over the night-period in stand- 

 ing pools, as a phase of the same problem which was ultimately 

 responsible for driving fish out of the water to become amphibians on 

 the land. From the standing pool above the tide-range, to existence 

 wholly out of the water in damp air, or with the casual supply of 

 the ' region of the splash ' and possibilities of atmospheric precipita- 

 tions of 'freshwater,' is but a small departure. Familiar observation 

 and recorded data as to the existence of even massive algal growths 

 out of the sea, within the region of the splash, afford a general view 

 of such translation from the water to air ; in which, again, further 

 adaptations for increasingly drier conditions, to be ultimately ex- 

 pressed by perennation in a state of even practically complete desicca- 

 tion, follows a natural sequence of xerophytic progression. The 

 existence of seaweeds out of the sea, exposed to damp air, is suffi- 

 ciently familiar in the ordinary phenomena of the tide-range and the 

 Fuci of the Salt-marsh ; the limiting factor being not so much 

 desiccation in the case of subsaturated air, as the ultimate starvation 

 implied in restricted capacity for proteid- synthesis on removal from 

 the food-solution. Photosynthesis of carbofn'drate may be increased, 

 and so prove excessive, since this alone is useless for continued growth ; 

 but a relatively very small amount of photosynthetic tissue, associated 

 with sufficient chances of obtaining the necessary food-salts, mav 

 solve the problem, not only in subsaturated air, but also under drier 

 conditions. Once it is clear that material for proteid-synthesis is of 

 even greater consequence than water-supply, the way is prepared for 

 xerophytic adaptation to economize the latter ; but no xeromorphic 

 adaptations are of avail in absence of food-salts. Hence once removed 

 from the sea- water, even the Lichen -association can be but a starved 

 production, and cannot lead to any very great development of the 

 soma. Desiccation may be faced, but not entire lack of food-salts, 

 whether owing to fresh- water environment, or failure to establish 



