TUE LICHEN LIFE-CYCLE 145 



paralleled in Aglaozonia^-, 8 (32-16), and in Zrinartl/nia", 4, following 

 increased volume of the flagellated zo'ids ; but the production of 

 immotile spores, replacing flagellated zo'ids, is the commonplace of the 

 Phseophycean Dictyota, as also of the tetrasporangia of the Floridese. 

 Tt is thus easy to see behind the normal production of a simple 

 apothecium the last vestigia of the morphological details of a mechanism 

 initiated in response to the biological factors of the sea • and there is 

 not the slightest reason to assume gratuitously that such features can 

 be ever reconstituted de novo, under any other set of biological factors, 

 merely because in the present condition of the world it has become a 

 commonplace of transmigrant organism. 



Similarly all phases of further elaboration of the asexual stage, as 

 it comes to be increasingly immersed in the parental tissue, protected 

 beneath the surface in perithecial chambers, and provided with ostiolar 

 mechanism of control for the regulation of spore-dispersal — constitut- 

 ing the organization of the conventional series of the I^renomycetes, 

 as opposed to apothecial Discomycetes, — are again mechanisms of 

 marine inception. Identical phases are traced in existing Florideae, 

 in which all such problems of the nutrition of countless ' cystocarps,' 

 on or in the branches or laminae of the parental soma, work out the 

 same features of physiological and morphological organization. Again, 

 in a manner which admits of no other interpretation, but that all 

 plants presenting such construction must have had the same initial 

 stimulus, and the same effective benefit, in order to establish the 

 same homoplastic result ; though now the spores of the Fungi may 

 be normally wind-borne, and present the cuticularized exospore of 

 subaerial vegetation ; later xerophytic adaptations of the land being 

 superposed on an older marine mechanism. 



That minor variations on such a theme should occur — as, for 

 example, complete failure of the perithecial wall to give the ostiolar 

 mechanism to a decadent cleistocarpic construction — need excite no 

 special remark ; nor again that the most minute and extreme cases 

 of holoparasitism on the leaves of higher plants shoiild give reproduc- 

 tive organs reduced to the limit of the uninucleate stage, or an asexual 

 phase with only a single ascus (Sphcerotheca). Such would be the 

 normal progression of deterioration, and the extreme nature of the 

 biological factors supplies a sufficient cause. Similarly the complete 

 loss of differentiated sexual organs in a mechanism now wholly auto- 

 gamous is intelligible, as also all conditions of apogamy, parthenogamy, 

 and pseudogamy 4 . 



1 Yamanouchi (1912), Bot. Gazette, 54, p. 472. 



2 Yamanouchi (1913), Bot. Gazette, 56, p. 23. 



3 There is in fact no knowledge of how a plant could be evolved on the land 

 only as a true ' land-plant,' when it is accepted that all land-life, both plant and 

 animal, must have been transmigrant. 



4 Guilliermond (1912), Re I Progressns, pp. 491, 493. 



(To be continued.) 



