V] LABOULBENIALES i8i 



the inferior sterile cell, the secondary inferior sterile cell, the mother-cell' 

 of the ascogenic cells and the superior sterile cell. The subterminal of these 

 alone gives rise to asci ; this it does by dividing longitudinally into a definite 

 number of ascogenic cells from which the asci are budded out. 



A multicellular trichogyne is not uncommon among Ascomycetes, and 

 the division of the oogonium after fertilization into a row of cells is a 

 well-known phenomenon occurring among Plectascales, Erysiphales, and 

 Discomycetes. In most cases several cells of the septate oogonium give 

 rise to ascogenous hyphae, but in the Erysiphales only the subterminal 

 cell of the row does so. In Erysiphe this cell, which always contains at 

 least two nuclei, gives rise to several asci and differs from the sub- 

 terminal cell of the Laboulbeniales chiefly in the fact that the asci are 

 produced from short outgrowths instead of, as in Stigmatomyces and its 

 allies, from daughter cells formed by longitudinal division. In this character 

 then, the Laboulbeniales would appear most nearly to approach the Erysi- 

 phaceae, which they also resemble in the formation of the sheath from the 

 stalk cell of the oogonium, but they differ from them in possessing a tricho- 

 gyne, an organ not known in that group, where the antheridium comes into 

 direct contact with the oogonium. 



The Laboulbeniales and Erysiphaceae have also in common the uni- 

 nucleate character of their vegetative cells. 



In the structure of their ascocarp, opening as it does by a narrow aperture, 

 the Laboulbeniales approach most closely to the other Pyrenomycetes. 



The male element in the Laboulbeniales is a non-motile, uninucleate 

 structure which may be budded off externally from the parent cell, or 

 extruded from it as a naked mass of protoplasm. 



Amongst the Fungi spermatia occur in the Pyrenomycetes and Lichens 

 and also characterize the Uredinales, but in all these cases they are budded 

 off externally as walled structures. The spermatium both in the Red Algae 

 and in the Fungi has been homologized with a reduced antheridium, and, 

 as has already been pointed out, the exogenous male element no doubt 

 bears the same significance among the Laboulbeniales. We have no satis- 

 factory indication as to the relative primitiveness of the endogenous and 

 the exogenous condition, but it may be noted that exogenous forms only 

 are known among Fungi other than Laboulbeniales. The endogenous organ 

 may be derived from the branch which cuts off exogenous, walled spermatia, 

 or it may represent quite a different response to the need for non-motile 

 male elements, the parent cell being the homologue of the antheridium and 

 the fertilizing element that of a spermatozoid. 



These various characters, approximating to those of sometimes one, 



' This cell is described by Thaxter as the ascogonium. The word has acquired a somewhat 

 different sense in other Ascomycetes. 



