THE LICHE> T LIFE-CYCLE 199 



adspersa l , with even the additional faculty for throwing out basal 

 disc-lobes of approved disc-soma habit. Earlier stages of develop- 

 ment also figured 2 are approximately identical with the ontogeny 

 of the multiseptate cable-type of Chorda Filum 3 . The relation of 

 these somatic data to the commonplace form-factors of marine 

 alga? is so striking that it is bevond equivocation, once it is grasped 

 that there must be a cause for the initiation of every such detail and 

 variant in somatic constitution ; and, again, that the effective cause 

 must he the same in all groups. So that when the marine origin of the 

 sea-weeds of the sea is accepted, the immediate marine origin of 

 the Laboulbeniacese is beyond question. As Lichens exemplify all 

 the various form-factors of the massive algal somata of the sea 4 , 

 so the Laboulbeniaeese present indications of all the corresponding 

 form-factors of the older filamentous soma 5 ; and, again, these and 

 no other. The problem presented to the mycologist, in the latter case, 

 is identically the same as that offered to the lichenologist in the 

 former. If these form-factors can be evolved de novo in a parasitic 

 fungus-race of the land, the initial stimuli to which they are the 

 response require to be demonstrated, as also their effective benefit. 

 One gets no further by concealing the details of construction under 

 terms of ' appendages of reproductive receptacles ' 6 , or postulating 

 'opportunities for eccentricity of form' 7 . Nor are the beautifully 

 segmented little bilateral frond-systems of Dichomi/ces 8 to be explained 

 as teleologically adapted to lie flat against the body of the host. 

 The alternative deduction that identity of form-factor, however 

 obscure or vestigial in individual cases, implies a common origin in 

 the sea is scientifically more satisfactory ; as again indicating the 

 heritable continuity of morphological detail when once established by 

 natural selection, even from a horizon that may be expressed by 

 thousands of millions of years ago. The conception of a successful 

 mutation, that once gained may be constant for ever (De Vries), is 

 the nearest thing to it in modern botany. Hence, while the marine 

 ancestry of the somata of the larger saprophytic fungi of the land 

 may be traced in the retention of skeletal hyphae of larger algal 

 growth-forms, and evidence of older cortical ramalia -systems may be 

 traced in more conservative reproductive organs, — the Laboulbeniaceaa 

 serve to mark the extent to which a similar high-grade soma may be 

 reduced to the earliest juvenile expressions of similar marine pro- 

 gression, as these present precocious reproductive capacity 9 . Just as, 



1 Sauvageau (1899) Ann. Sci. Nat. p. 325. 



2 t. 23 (1896) p. 372, a more definitely aquatic form, 1 mm. 



3 Reinke (1892) Atlas, t. 28 ; Batters (1895) Ann. Bot. p. 307, Buffhamia. 



4 ' The Lichen Symbiosis,' Journ. Bot. 1920, p. 265. 



5 'The Phaeophycean Soma,' Bot. Memoirs, 1920, p. 24. 



6 Thaxter (1896) Monograph, pp. 206, 208, ' of systematic value only.' 



7 Thaxter, loc. cit. p. 198. 



8 Thaxter (1908), p. 226. 



9 Even De Bary missed the significance of the ' appendage ' of Peyritsch. 

 although noting that it was produced from the apical unit of the biseptate spore 

 in Stigmatomyces (De Bary, 1887, Eng. Trans, p. 264) ; and Faull (1912, p. 330) 

 seems struck by the fact that the ' appendages ' do not show signs of decay, but 

 are well-nourished even on old plants ! 



