Journal of Agricultural Research 
Yol. XXVIII, No. 10 
ieucospermum which occurs frequently in the vicinity of Moscow and which 
Kursanov (6) finds has sori with chains of uninucleated aecidiospores. No cell 
fusions take place at their origin. The spores germinate like the ordinary aecidio- 
spore, except that the germ tube has one nucleus instead of two. The spores 
with two nuclei are much larger than those with only one, whereas Moreau {12, 
p. 182 ) found that the uninucleated spores of her Endophyllum corresponded 
in size with those described for the species. Occasionally a spore in one of the 
chains is binucleated. Such a case is clearly the result of a nuclear division. 
Where a chain of binucleated spores is found in a sorus the possibility of a cell 
fusion at the base is not precluded. 
Lindfors {9) has more recently given a most interesting series of brief discus¬ 
sions of life histories of certain rusts. He has signally departed occasionally 
from the practice of trying to make what he finds in his material conform to the 
commonly accepted notions of cell fusions and to the doctrines relating to the 
fixity in rust cycles. For example, he finds that in Uromyces acetosae the first 
telia develop close to the aecidia. He figures an aecidium and a telium arising 
out of a common uninucleated mycelium. He also claims that the binucleated 
condition is not limited as to its origin, to cell fusions at the base of a sorus. 
Although cell fusions occur in Puccinia arenariae, without spermogonia, the 
promycelium has only two cells. Two binucleated sporidia are formed. 
Up to the present time one of the greatest obstacles to the understanding of 
the workings of evolution in the Uredineae is our proneness to believe in the 
fixity of what are called genera and species. Owing to the immediate need for 
some systematic treatment of rust parasites, which were being discovered attacking 
our economic plants, much of the preliminary work, of necessity, has been based 
on dried material. Furthermore the cytological work has mostly been confined to 
a study of the so-called sexual fusions. The desirability of gathering, for fixation, 
material obtained as the result of extended culture work was clearly not of prime 
necessity in those days when Blackman and Christman were making their dis¬ 
coveries relating to nuclear migrations and cell fusions occurring at the origin 
of the aecidium. Moreau and Kursanov did not supplement their cytological 
work on uninucleated aecidiospores with culture work, and nothing was said 
regarding the presence or absence of spermogonia in those forms. Judging 
from Moreau's figures of the promycelia, which do not show any nuclei, it would 
not be surprising to find that if the uninucleated spores of that Endophyllum 
were germinated Under conditions sufficiently normal to lead to the formation 
of sporidia, the promycelium would be found to be regularly 2-celled with one 
nucleus in each cell. 
Blackman ( 1 ) saw in the sterile cell above one of the fusing cells the ancestral 
red alga trichogyne, and he saw in the migrating nucleus passing up into the 
basal cell (the “egg cell”) a substitute for the now functionless spermatium. 
This view has long been discarded. In all of the more or less deep-seated 
aecidial primordia the fusing cells are in reality merely intercalary cells of the 
stroma-like, space-making, and food-storing hyphal plexus. The fusions are 
of exactly the same nature as are those occurring between the accessory sterile 
and auxiliary cells in the red algae. The resultant is the accumulation of mate¬ 
rials and vigor for the building of numbers of reproductive spore bodies. 
Christman’s (2) suggestion that the cell,fusions occurring between two equal 
-cells must represent the sexual fusions of the ancestral Spirogyra-Mucor of the 
Conjugateae, while not generally accepted in this particular sense, nevertheless 
has gone far to establish firmly in the literature the terms sexual cells (gametes) 
and sexual fusions for those purely secondary fusions occurring between cells 
which have no homologies whatever to sexual organs, spermatia and oogonia, of 
any possible ancestral form. 
