The Cytology of the Uredinece. 75 
that the primary uredo pustules are accompanied by spermogonia. 
On the other hand the secondary uredo pustules are not accompanied 
by spermogonia. Winter in fact surmised in 1884 that the primary 
uredo pustules of Brachy-puccinia represented the aecidia of other 
forms. Christman now finds that the primary uredospores of 
Phragmidium potentillce canadensis arise from basal cells which 
become binucleate in the same manner as that described for the 
basal cells which give rise to the chains of aecidiospores in 
Phragmidium speciosum. These basal cells in the primary uredo 
pustule of the above species of Phragmidium form spore mother 
cells, each of which by division produces a spore and a small sterile 
cell which elongates to form the stalk of the primary uredospore. 
A second spore and stalk are produced by the putting out of a bud 
from the basal cell and subsequent division. Christman identifies 
the stalk of the primary uredospore with the intercalury cell of the 
aecidiospore. 
More recently Olive 1 has confirmed for Triphragmium ulmariiz 
the view that the primary uredospores of Brachy-forms correspond 
to aecidial stages of other types. In the Micro-forms, Pucciuia 
transformans, i.e. a species possessing only teleutospores, he finds 
that the basal cells which produce the teleutospores, arise by the 
fusion of two uninucleate cells, so that the origin .of the teleutospores 
of this species may be said to be similar to that of the aecidiospores 
of other forms. 
Christman finds also that the secondary uredospores, also of 
Phragmidium potentillce-canadensis also arise from large basal cells 
though of course in this case the latter are borne on a mycelium of 
binucleate cells. The teleutospores of Puccinia podophylli arise 
also from large basal cells. These large basal cells in the developing 
uredo- and teleutospore pustules have also been described by 
Blackman in his work on Phragmidium violaceum. 
Christman is impressed with the similarity between the basal 
cells from which the uredo- and teleutospores originate and those 
which give rise to the aecidiospores. He considers therefore that 
the basal cell is the morphological unit to which may be referred 
all the other spore forms of the sporophyte generation. According 
to this point of view teleutospores, aecidiospores, and uredospores 
would all be considered secondary structures. That there is some 
essential connection between these spore forms would appear to 
follow from a consideration of such a genus as Endophyllum in 
which the teleutospores are abstricted in the same manner as the 
aecidiospores of other genera. 
In the paper by Olive cited above, an account of the cytological 
investigation of the origin of the chains of aecidiospores of other 
forms is given. Most of this work concerns the Caeoma-type of 
aecidium with which Olive includes the primary uredo spore 
generation of the Brachy-forms alluded to already. Olive finds 
that the binucleate condition arises by the conjugation of two 
uninucleate cells. In the process of fusion the nucleus and cyto¬ 
plasm of the one cell pass into the other cell by means of a pore of 
greater or less width. Olive mentions the difficulty experienced in 
1 Olive, F. W. .Sexual Cell Fusions and Vegetative Nuclear 
Divisions in the Rusts. Annals of Botany, 1908. 
