Be ae ee OTE Nd te SO Ege ROE, Pee ee 
Ce keane te Oe ee ort Pan Pe A eS ae 
sa far ytd Eo 
1906] OVERTON—THECOTHEUS PELLETIERI 481 
division and a double reduction is necessary to accomplish the same 
results. This triple division of the ascus nucleus occurs universally, 
whether two spores, four spores, or eight spores are to be formed. 
HARPER has pointed out how fundamental this triple division is, since 
when only two spores are to be formed, as in Phyllactinia, six nuclei 
degenerate. In such cases the three divisions constitute a single con- 
tinuous process. That all these divisions persist, no matter how many 
spores are to be produced, shows their necessity in the process of 
reduction. 
The work of BLrackMAN (:04) and his students (:06) and of 
CHRISTMAN (:05) have established an undoubted alternation of 
generations in the rusts, showing that in these forms the series of 
binucleate cells originate as a result of fertilization. The gamete 
nuclei persist throughout the sporophyte generation as independent 
nuclei, dividing by a conjugate division. In the teleutospore these 
nuclei fuse, and a synapsis stage occurs, followed by a double division 
which leads to the formation of the four nuclei of the four sporidia. 
As Harper suggests, there is a striking parallelism between the teleu- 
tospore and the spore mother cell of the higher plants. He believes 
we are justified in regarding the first and second divisions in the 
promycelium as respectively heterotypical and homeotypical. As 
there is only one nuclear fusion in the life cycle of the rust, a conse- 
quent double division occurs in reduction. Marre (:05), finding 
in Galactinia that certain of the cells of the ascogenous hyphae which 
give rise to the asci are binucleate, holds to the conception that these 
binucleate cells correspond to those of the Basidiomycetes as well as 
to those of the rusts. There should be a series of binucleate cells in 
the sporophyte in all these groups, whose nuclei should divide by 
conjugate division, fusion first taking place in the basidium, in the 
teleutospore, and in the ascus, each of which would be comparable 
to the spore mother cells of the higher plants. This explanation 
does not explain, however, the universal occurrence of the third divi- 
sion, which is so general among the Ascomycetes, and which FauLt 
has found to occur in the Laboulbeniaceae; nor does it account for 
the apparently secondary nature of the fusions described by BLAcK- 
MAN and CHRISTMAN, as compared to those of the red algae, lichens, 
mildews, and Pyronema. It is certainly of great importance to know 
