2GG TKE JOURXAL OF BOTANY 



construction, to depauperated sea- weeds is so striking that it cannot 

 be blinked in the case of the finer types of the Lichen-series. Though 

 minute and microscopic forms may show fewer characteristics, there 

 are also many equally reduced relics of Florideae and Phajophycese in 

 the sea which retain little special somatic organization. It is to the 

 fmest and most complex types that one must look for the culminating 

 expressions of response to the environment which has produced them. 

 Decadence and extreme impoverishment prevail in tide-pool vegeta- 

 tion, and every grade of rudimentary organization that is not neces- 

 sarily * primitive ' may be found in the sea ; while the very mode of 

 life of a lichen implies the added precariousness of existence, as 

 inclining the organism to all ultimate phases of somatic degradation. 

 Admirable illustrations are given by Reinke (Prings. Jahrb. xxvi., 

 xxviii.) — there is no need to multiply types : a dozen will suffice, cf.: — 

 Cladoniafurcata (xxvi. p. 505), C. o'etipora (p. 506), C. verticillata 

 (p. 509), Lecanora escidenta, L. fruticulosa (xxviii. p. 372), Rama- 

 Una Eckloni (p. 378), B. farinosa (p. 379), Parmelia reticulata 

 (p. 383), P. liottentotta (p. 384), P. arizouica (p. 385), Getraria 

 (jlauca (p. 389), Evernla furfuracea (p. 392), JJsnea Taylor i 

 (p. 396), Sticta latifrons (p'. 441). 



lleinke (1895), as an algologist, naturally recognized the many 

 striking points of similarity in external mor])liology to quite ordinary 

 types of Floridese, even including calcified forms asLithothamnions. 

 His conclusions, however, that such growths will illustrate the parallel 

 progression of plant-somata in response to the same physiological 

 ])roblems, affords an admirable example of utilizing conceptions of 

 homoplasy to beg the question. There is, in fact, little identity 

 of biological factors or physiological mechanism in the case of a 

 lichen growing on a rock exposed to air and a submerged alga of the 

 sea. According to Reinke (1895, p. 100) the principles to which the 

 Lecidean type of thallus affords the response are suggested as : — 



(1) The form and structure of the consortium in relation to 

 CO^-metabolism. 



The protection of the gonidia (from desiccation — certainly not 

 from starvation or death by exhaustion). 



(3) The formation of reserve-storing tissue. 



On the other hand, the sea-weed soma has little reference to these 

 factors, since (1) the CO^-metabolism of the sea is on an entirely 

 different footing as regards both amount and quality of the light and 

 gas-supply; (2) the xerophytic factor is wholly wanting, and there is 

 no question of protection from desiccation in the sea ; (3) stores 

 of reserves may be illusory, just as algse may accumulate large 

 amounts of polysaccharide and carbohydrates of sorts merely as the 

 expression of starvation for lack of nitrogen. 



The sea-Aveed soma represents the response of autotrophic life to 

 such factors as (1) surface-exposure to the external medium and light 

 of as many photosynthetic units as possible ; (2) mechanical efficiency 

 in avoiding the drag of a moving medium. Laminate expansions 

 and systems of ramification represent the means of supplying the 

 former ; texture, cohesion, and strength of axes the latter. Marine 

 algse are also filamentous, gelatinous, massive, or calcareous; such 

 ty])es of soma being the response to special conditions of marine 



