892 
Journal of Agricultural Research 
Vol. XXIV, No. II 
cells at the center or apex are beginning to disorganize and collapse at 
their lower ends (PI. i, A, and 5, B). As the peridium is lifted these 
central cells sustain considerable pressure from the sides so that they 
eventually become distorted, compressed below, enlarged above, and are 
finally thrust somewhat out of place as they break through the epidermis. 
The spinelike thickenings which are being formed during the rupturing 
processes may in some way facilitate the final dislodgment of the peri¬ 
stomal cells in older sori. The cell ps in Plate 4, E, is slightly more than 
half the length of that of the adjacent peridial cell, p. Originally these 
two cells were the same length; therefore, the difference seen later is due, 
not to the thickening of the wall of the lower end, as thought by Far- 
low, but to disorganization which is not confined to the peristomal cells 
alone. It is interesting to see that while the lower end of such cells is 
becoming disorganized and distorted the cytoplasm and nuclei in the 
upper part are still active, holding the gentian violet s-tain to the last 
or until the spines are formed. 
It is now a well-recognized fact that peridial cells of an aecium 
are the homologs of aeciospores, being merely the specialized terminal 
cells in the chain of spores. The figures in this paper suggest that these 
homologies can be carried over to the uredinium of Pucciniastrum, 
where the peridial cell and intercalary cell below are comparable to the 
uredospore and its stalk, which supports the theory first advanced by 
Sappin-Trouffy (ij, p. 86) and further defended by Christman (4). 
Stalked spores arising from budded basal cells were not found in the 
limited study of P. hydrangeae made by the author. Such types as are 
shown in Plate 5, I, suggest that in older sori the intercalary cell may 
elongate to take the forru of a stalk and that the basal cell may bud the 
same as we find in the other species. 
It is a certainty that spores are sometimes fonned atypically in P. 
americanum^ so the author has hesitated to interpret the figures in Plate 3, 
which show (at the right) spores without stalks or supporting intercalary 
cells. The author has relied on the positive evidence offered by finding 
intercalary cells and pedicellate spores in just such sori, rather than on 
such negative evidence as these figures might be interpreted to afford. 
In the orderly process of spore formation in uredinia there is a hymenial 
layer of basal cells from which spore initials regularly arise, but all sorts 
of abnormalities are liable to occur here as in other fungi, so that a spore 
might be formed from almost any cell, peridial, intercalary, or basal. 
Every well-nourished cell in the primordium is potentially sporogenous, 
but usually one of the daughter cells of the spore initial is in effect 
sacrificed, thus providing additional food for the one that is to become 
the spore; the other, although incidentally becoming a disjuncting 
intercalary cell or an elongated stalk, finally degenerates.'* 
Magnus' figure 7, Plate XIV (12), in support of his view is not con¬ 
vincing. He may have overlooked the stalk cells or their homologs, 
intercalary cells, as he did the peridial cells in Hyalopsora which Bar¬ 
tholomew (j) shows very plainly to be present in this genus. Ludwig 
* I^. Kursanov, in a recent paper which has jitst come to hand (Recherches morphologiques ct cytolo- 
giques sur les Uredindes. Bui. Soc. Nat. Moscow, y. 31, p. 1-129, pi. 1-4, 25 fig. Oct., 1922), traces the de¬ 
velopment of terminal sterile cells in the uredo sori of Puccinia allii, Triphragmium ulmariae, Uredo {Puc¬ 
ciniastrum) pirolac, and Hyalopsora polypodii-dryoptertdis. He figures intercalary cells directly beneath 
the sterile terminal cells in the last two species and states that they arise by the division of the subterminal 
cells. This may very well be their method of origin in the species of Pucciniastrum which the writer has 
imder discussion, but it would not aiBfect their homology. Instances of the cutting off of the intercalary 
cell from the upper part of the aecidiospore initial are well known. Kursanov has not followed fully the 
development of the uredo spores in Pucciniastrum pirolae, so that the reader is left in doubt as to whether 
they are provided with true stalk cells or not. 
