THE LICHEN LIFE-CYCLE 197 



THE LICHEN LIFE-CYCLE. 

 By A. H. Church. 



(Continued from p. 170.) 



V. The Case of the Laboulbeintace,e. 



The remarkable forms of the Laboulbeniacea? are described more 

 particularly in the classical monographs of Thaxter 1 , and are now 

 enumerated to about 50 genera and 600 species ; though they are 

 still little known in complete cytology, and are largely lacking in 

 interpretation. These diminutive fungi, holoparasitic on insects (as 

 beetles and Hies), reduced to a minimum somatic expression, being 

 rarely over a millimetre in height, as the merest vestigial pulvinate 

 types of thallus, present a complexity of fertilization-mechanism 

 which, in some respects, takes them even far beyond the horizon 

 of the Floridese of the sea. Yet, fundamentally, they agree in 

 a primary scheme of a two-phase life-cycle, fertilization in situ, a 

 diploid asexual sporangiate phase bearing the familiar 8 (4)-spored 

 sporangia, hence termed ' asci ' (commonly reducing to the limit of 

 4 spores, and these biseptate), so that the family is still convention- 

 ally included within the great Fungus-series of the Ascomycetes 2 . 



The sporophyte generation is reduced to the barest minimum of 

 2-3 supporting cells, from which asci are budded off (only in an 

 extreme case as many as 30), and the asci present the familiar scheme 

 of meiosis, followed less frequently (Compsomyces, 3foscJio?nyces) by 

 one mitosis to give a series of 8 ascospores. The last mitosis is 

 commonly suppressed, giving the limit of one tetrad ; and the 

 septation of the spore-origins may follow on after the laying-down of 

 the spore-coat, giving the case of the septate spore with a limiting 

 expression commonly obtaining as the biseptate condition. Spore- 

 discharge is graded by successive growth of asci, and controlled by 

 close-fitting ' perithecial ' mechanism with narrow ostiole, which 

 often represents the greater part of the parental gametophyte, to 

 such an extent that the significance of other portions of the soma has 

 been obscured b} r the use of the expression 'receptacle ' 3 . In these 

 respects the Ascomycete-relations of the Laboulbeniacea? appear 

 bevond dispute ; they express the miniature vestiges of a cellular 

 perithecial construction, again the more interesting as the perithecium 

 with its ostiole is in functional operation before fertilization and the 

 production of the asexual spore-output it was originally designed to 

 control. Exactly as in the case of the higher Floridea?, the wall of 

 the cystocarp may be precociously conspicuous before fertilization 

 (cf. ' Ceramidia ' of PolysipJionia, Gorallind). The hymenialoigan- 

 ization is wanting 4 ; there are no parental paraphyses, and the asci 



1 Thaxter (1896) Monograph of Laboulbeniaceje, I ; (1908) II. Faull (1911) 

 Annals of Botany, p. 649: (1912) p. 325. Guilliermond (1912) Rei Progressus, 

 p. 487. 



- fetrasburger (Eng. Trans. 1912) p. 388 : Fanll (1912) p. 344. 



3 Thaxter (1898) Monograph I, p. 206. 



4 Thaxter (1898) Monograph II, p. 231, t. 37; distinctly suggested in 

 Polyascoivyecs with exceptional number (30) of ascogenous cells. 



