Laboulbenia chaetophora and L . Gyrinidarum . 345 
been more than superficially investigated. Turning to the species described 
in this paper it will be seen that the observations noted do not bear out 
either of these views. The fusion of the nuclei in the young ascus is the 
only nuclear fusion found in the life cycle ; there is but one rneiosis ; and 
conjugate divisions play an important part. 
Relative to the problem of the sexuality of the Ascomycetes it is be- 
coming increasingly obvious that the phenomenon of conjugate divisions 
must be given serious consideration. The regularity of their occurrence 
among the Laboulbeniales is certain, and there is a growing body of evidence 
pointing to the generality of the phenomenon throughout all but one or two 
other subdivisions of the sac-fungi. That this feature has either been 
inherited from an earlier stock, or that it has been evolved within the 
Ascomycetes themselves, is self-evident. In either case, it would not be 
wholly unexpected to find occasional reversions to the more primitive pro- 
cedure of a fusion of gamete nuclei directly following the conjugation of 
sexual cells. Such fusion nuclei would be potentially capable of at once 
forming spore-nuclei. It is understandable that sometimes, as Claussen 
asserts is true in Pyronema , there might be nothing more than pseudo-fusions 
in the gametangium, the actual fusions taking place normally in the asci. 
Such reversions would explain the recorded instances of fusion in the female 
gametangium, and the fallacy of assuming — what has never been demon- 
strated — that the sexual act comprises two successive nuclear fusions. The 
same tendency would also account for pseudo-fusions. In view of the need 
of research on the nature and extent of conjugate divisions in the Ascomy- 
cetes, especially because of the light an exact knowledge of this feature 
will throw on the problems of their sexuality and phylogeny, I venture 
to review the field and to explain the grounds taken above at greater 
length. 
Cytological investigations on the higher Fungi in recent years have 
uncovered the interesting and universal phenomenon of a fusion of two 
nuclei in the spore mother-cell. An even more remarkable fact has been 
established for all but the Ascomycetes in this connexion, namely, that the 
fusing nuclei belong to two distinct lineal series the members of which have 
lived side by side in pairs, dividing conjointly without fusion for many 
generations. 
Dangeard (’93), Sappin-Trouffy (’93 and ’96), Blackman (’04), Christman 
(’05 and ’07), Blackman and Fraser, (’06), and Olive (’08) have cleared the 
ground in the case of the Rusts. They have shown that a binucleate phase 
begins with the migration of a nucleus from one cell into another at a definite 
stage in the life-history, and that the progeny of these initial pairs accom- 
pany one another uncombined up to the teleutospores, where fusion ensues, 
followed at once by a reduction division. These events indicate that a curious 
type of sexuality has been evolved in the Rusts, one characterized by a long 
