THE LICHEN LIFE-Cl'CLE 201 



meiosis undoubtedly normally obtains in the ascus l , the sexual plants 

 ai-e presumably haploid. Fertilization of the female gamete, though 

 not yet traced in full cytological detail, is more complex than in the 

 Floridean. The carpogonial branch is remarkably constant, as again 

 indicating the retention of some very anciently established mechanism. 

 The carpogonial cell is a uninucleated little-differentiated basal unit, 

 with supei'posed ' trichophoric cell ' similarly uninucleate. This in 

 turn bears the so-called ' trichogyne,' as a mere hair-extension 2 , or as 

 a copiously branched system of uniseriate ramuli, the end-units of 

 which may be spirally coiled 3 , giving a plumose effect for the collec- 

 tion of passive spermatia, much in the manner of the plumose pollen- 

 collecting stigma of a grass, and similarly devoted to the retention of 

 one fertilizing unit. The essential point is that in process of reaching 

 the female nucleus, the male nucleus must inevitably travel via a 

 sequence of cell-segments of the trichogyne-system, when this is 

 multicellular, and in all cases through the trichophoric cell, opening 

 up the primary pit-connections in its passage, in a manner which 

 recalls the post-sexual migration of the zygote- nucleus of higher 

 Floridese, but is here pre-sexual to an extent which does not obtain 

 in any known algal form ; though it is undoubtedly also the mechanism 

 of sexual approximation in the Lichen. Precise cytological details 

 may be still wanting for the Lichen-type ; but the case of Collema 

 (Baur) and Physcia (Darbishire) is clearly but a variant on the 

 mechanism of Laboulbenia (Faull) 4 ; again, by no means exactly 

 homologous, but directly analogous as spermatogamy prevails, and an 

 indication that the same biological progression has been followed 

 through successive stages in plant-phyla of presumably widely diver- 

 gent descent. The analogy is the expression of parallel adaptation 

 to similar conditions of environment, and is not to be taken as indic- 

 ative of any direct ' affinity.' 



The Laboulbeniaceae, so unlike the saprophytic Ascomycetes of 

 the land, and somatically clearly of marine origin, thus serve to 

 complete the halting tale of the Lichen-Fungi, and so bridge the gap 

 of the otherwise inexplicable vestigial uniseriate procarp. There 

 can be no reasonable doubt that the convergence of these remarkable 

 and residual groups of heterotrophic plant-organism is the expression 

 of a common origin in the sea, following the opportunities of tide- 

 pool formations for a restricted plankton-rate in cheap spermatia, the 

 wholly protected and controlled production of female gametes without 

 wastage, and the graded output of asexual spores capable of with- 

 standing the desiccation of subaerial translation. The larger group 

 of Asconvycetes in the narrower sense, adopting methods of sapro- 

 phytic nutrition on decaying remains of vegetation, passes in the 

 limit to active holoparasitism on the photosjmthetic tissues of the 

 foliage-leaves of higher land-plants. The Lichens survive in virtue 

 of their association with intrusive algal scums in ill-aerated shore- 

 ponds. The Laboulbeniacese, having passed through the stages of 

 saprophytism on dead organisms to obligate parasitism on the smallor 



1 Faull (1911) Ann. Bot. p. 652. 



2 Thaxter (1896), Zodiomyces, t. 23, fig. 16. 



3 Loc. cit. t. 2, fig. 5 ; t. 21, fig. 15 ; Faull (1912), fig. 31. 



4 Faull (1911), p. 651. 



Journal or Botany. — Vol. 59. [Jt*ly, 1921.] p 



