Ill THE JOURNAL OF BOTANY 



any possibility of cross-fertilization. An older condition of oogamic 

 fertilization in situ (conceivably on the lines of Aclilya, still with 

 many oospheres) has been superseded in favour of autogamous siphon- 

 ogamy by means of a conjugation-tube 1 . With the deterioration of 

 the sexual units, fertilization -mechanism is reduced to the merest 

 expression of the pairing of conjugate nuclei and the production of a 

 communal zygote ; the essential features of karyogamy being indi- 

 cate 1 to the extent that the developing zygote may he still regarded 

 as a diploid phase. It is sufficiently clear that however residual the 

 phenomena of syngamy, the method is only a deteriorated version of 

 the familiar algal prototype, in which similar organs once emitted 

 flagellated zoid-gametes in the plankton-phase of the free medium of 

 the sea. So far is the common story of the text-hooks 2 . 



The further development of the alternating asexual stage Csporo- 

 phyte), follows lines of complete parasitic decadence and dependence 

 on the parental mycelium. The entire strength of the organism is 

 devoted to the reproductive function, and asexual sporangia in which 

 meiosis has been intercalated, express the first limiting phase of 

 reduction in spore-output, as the two divisions of meiosis are followed 

 by a limit of one normal mitotic division only, giving a total content 

 of eight spores •". The collocation of such sporangia in a hymenial 

 layer is but the commonplace of algal construction (Chorda, Lain i- 

 naria) ; the provision for continual output of new asci, maintaining 

 the level of the older units is ingenious in its cytology, but the inter- 

 calation of meiosis in such asexual organs again follows similar sea-weed 

 rules (as in Aghtozonia). Not only is the reduction of output directly 



1 The fact that the conjugation-tube is produced by the oogonium, and not by 

 the antheridium as in Pythium and Saproleyrtia. lias led to the suggestion of its 

 being a vestigial ' trichogyne.' A trichogyne with functionless spermatia is 

 found in Polystigma (pseudogamous), and a more definite one of 4-6 cells in 

 Lachnea (parthenogamous). There can be also no doubt that many types pre- 

 senting- • Wbronin's hypha ' have lost a triehogyne-mechanism [ci. Xylaria) ; so 

 that different methods of fertilization obtain within the conventional group, and 

 express the secondary nature of these processes. But while there can be no 

 question as to the decadence of the mechanism, the point remains as to what was 

 the prototype of which these phenomena are such highly modified vestigial ex- 

 pressions. Noting- again that it is not parasitism per se but autogamy which 

 induces deterioration in the sexual process ; parasitism only affects the somatic 

 tracts. 



2 Strasburger (Eng. Transl. 1912), p. 380, Monoblepharfa. 



3 The remarkable capacity of the eight spores of the ascus for further septa- 

 tion always attracts attention, particularly as it is equally characteristic of the 

 ascospores of Lichens and Laboulbeniacese, though wanting in the unilocular 

 sporangia of the sea ; while it is equally clearly not the expression of precocious 

 germination. The solution of the problem appears to lie in the fact that the 

 ' spore-origins,' which invest with a firm spore-coat, are delimited after the first 

 normal mitosis, and whatever subsequent mitoses occur, the number of primary 

 spores is determined by this early isolation of perennatiug units with the charac- 

 teristic spore-membranes of land-flora. From such a standpoint the precocious 

 initiation of the exospore of land-flora, which takes some time to differentiate, 

 introduces a time-factor into the progression. Admitting such septation as 

 normally continued, the biseptate spore would be a limiting case : such biseptate 

 spores are characteristic of many small Ascomyeete types (Mycosphserella) and 

 Lichens (Physcia), and become the general rule in Laboulbeniacea.'. 



