344 
Fault. — The Cytology of 
strongly developed at the upper end, the future basal cell of the plantlet 
into which the spore will grow should it find favourable lodgement on a 
suitable host. 
Discussion. 
One immediate result of these investigations has been the confirmation 
of Professor Thaxter’s classification of the Laboulbeniales as true Ascomy- 
cetes. This recognition is based on the characters of the spore sac. for the 
only positive diagnostic feature that distinguishes the Ascomycetes from 
other higher fungi is the ascus. That organ has been submitted to a very 
searching and successful examination during the past few years, so that our 
conceptions now concerning it when it is placed in comparison with the 
phycomycetous sporangium, the floridean tetrasporangium, or any other 
spore-bearing cell are no longer hazy. Every research has testified to the 
constancy of its nuclear heritage, and to the sureness with which certain 
characteristic cytological changes recur in the course of its development, all 
of which in combination suffice to distinguish it from every other spore- 
bearing organ known in the organic kingdom. Thus the unfailing inheri- 
tance of a pair of nuclei, the regularity of their fusion in the young ascus, the 
minutiae of the successive three mitoses, and the details of spore-delimitation 
by a remarkable method of free cell-formation are uniform throughout the 
group and without a parallel in any other. Precisely the same phenomena 
characterize the spore sac of the Laboulbeniales, in fact so exceptionless as 
to throw no new light on the origin of the ascus. This faithful cytological 
similarity, therefore, affords conclusive proof that the Laboulbeniales can no 
longer be counted among the doubtful Ascomycetes, or that the Laboul- 
beniomycetes of the Engler system can be maintained as a class, or that they 
can rank other than as an order or suborder of the sac-fungi. Unquestionably, 
in accordance with prevailing definitions, the Laboulbeniales, Thaxter, are 
rightly regarded as Ascomycetes and as a suborder of the Pyrenomycetes. 
Studies on the cytology of the Laboulbeniales have still another and 
very special interest in that they promise material additions to our knowledge 
of the sexuality of the Ascomycetes. This is a fascinating subject on its 
own account, and has also a wide bearing on the difficult problem of the 
phytogeny of the sac-fungi. 
There is a strong tendency at the present time to regard the Ascomy- 
cetes in point of sexuality as unique among plants and animals, for it is 
commonly believed that their sexual phenomena comprise two successive 
nuclear fusions, one in the female gametangium or its substitute, and the 
other in the ascus. This, if true, would involve a quadrupling of the chro- 
mosomes in the fully fertilized egg and a subsequent double reduction. 
There is likewise a tendency to deny the existence of normal series of con- 
jugate nuclear divisions in the Ascomycetes, though the subject has not 
