The Origin and Development of the Apothecium etc. 
419 
Boudiera, but now, aftcr further study of bis preparation, concludes that 
tliere is only a single fusion. As is well known, the higher ascomy- 
cetes liave been supposed to differ from all other groups of plants in that 
there are two nuclear fusions in their life history. Claussen’s conten- 
tion of a single nuclear fusion works out very nicely theoretically, since it 
brings these discoinycetes closer as regards the phenomena of fertilization, 
to the oomycetes, rusts, and higher basidiomycetes. But if there is only 
one fusion of nuclei, the nuclear divisions in the ascus remain a puzzle. 
Miss Fraser (36) described a second process of chromosome reduction 
which she termed “brachymeiotic” in Humana granulata. Her results 
were later confirmed in other species by Fraser and Welsford (38). 
Claussen finds no brachymeiotic division in the ascus and finds the 
same number of chromosomes in each of the tliree nuclear divisions. Be- 
sides the indirect evidence of two nuclear fusions in the life history of 
the fungus furnished by a brachymeiotic division in the ascus, there is 
the fact that in a very great number of ascomycetes eight spores are 
formed and that in cases in which less than eight spores are formed, eight 
nuclei are always formed, some of which later disintegrate. Claussen (20) 
seems to consider the formation of eight nuclei of no consequence and 
apparently thinks that the unimportance of the number of nuclear divi- 
sions is shown by the fact that in the genus Rhyparöbius the number 
of spores varies from 2 3 to 2 10 , also that in many ascomycetes the 
four or eight spores become multicellular. This explanation seems entirely 
inadequate. If it were possible to show that in a large number of cases 
only four nuclei were produced in the ascus, we might have some evidence 
against a possibility of two nuclear fusions. Claussen finds further 
ground for his argument in the fact that in some hepatics the spore mother 
cells divide more than twice so that several-celled spores result, and that 
in other hepatics the spores germinate witliin the sporange. All this 
seems inapplicable to the particular point in question. The fact remains 
that in all the higher ascomycetes which have been investigated no less 
than eight nuclei are formed in the ascus although some of thern may 
later disintegrate. The relation of the triple division in the ascus to a se- 
cond fusion in the life history of the fungus has been discussed by Harper 
(52, pp. 82, 83). Whether what we have called multicellular spores 
should be considered as resting stages in the development of the gameto- 
phyte is another question and has no bearing on that of a double nuclear 
fusion in the life history of the plant. 
I have no positive evidence of a fusion of nuclei in the ascogonium 
in Collema pulposum, although the position of the nuclei sometimes 
28 * 
