338 
Fault . — The Cytology of 
The Ascogenic Cells. 
The ascogenic cells are binucleate at all stages. The rather large 
nuclei divide simultaneously prior to the formation of each ascus (Fig. 37). 
This is a conjugate division : one of the daughters of each of the mother 
nuclei passes into the young ascus and the other remains in the ascogenic 
cell. The pair left in the ascogenic cell immediately begin to increase 
in size, and with the advent of the next ascus undergo another division. 
The divisions of the nuclei are homotypic, and, as has been seen to be the 
case elsewhere, the central bodies are conspicuous and the chromosomes 
four in number. In Fig. 39 a metaphase stage is represented in which the 
chromosomes are especially large and somewhat scattered, so that the count 
could be made with certainty. 
The protoplasm of the ascogenic cells, as of the procarp, is dense and 
very finely granular, and exhibits a greater capacity for stain than the cells 
of the perithecium and receptacle, so that they always stand out clearly 
differentiated from the rest of the thallus. 
The ascogenic cells of the Laboulbeniaceae have seemed to be unique 
among the Ascomycetes in respect to the limited and constant number for 
each species, and in respect to their capacity for giving origin to an 
unlimited number of asci. The number of ascogenic cells in Amorpho- 
myces and two or three other genera is one, in Laboulbenia and several 
others two, in Stigmatomyces four ; in Haplomyces there are eight, and 
in Polyascomyces there are thirty-two or more. This fixity of number 
is paralleled, however, by such genera as Sphaerotheca , in which there is 
a single ascogenic cell in every fruiting body, and as to the unlimited 
capacity of the ascogenic cells for ascus production I have found examples 
not at all uncommon in practically every order. The cytological details in 
these examples correspond to those in Laboulbenia in that a series of 
conjugate divisions takes place in the ascogenic cell in relation to a corre- 
sponding budding off of asci. Brefeld (’ 74 ) long since cited what has 
often appeared exceptional in the case of Penicillium , but theoretically 
at least his claims may be regarded as perfectly valid. The investiga- 
tions of McCubbin (TO) and Brown (TO, ’ll) have shown the same thing 
expressed in another way for Helvella elastica , Leotia , and Lachnea , 
namely, that the nuclei of a potential ascogenic cell may undergo many 
conjugate divisions, and eventually give rise to many asci. 
The common underlying principle is that of conjugate divisions, 
which is undoubtedly a character of the Ascomycetes. In Laboulbenia 
the apparatus involved is extremely simple, since the ascogenous cells 
correspond to the entire system of ascogenous hyphae and part of the 
female apparatus in most other groups. They are characterized by 
