652 Journal of Agricultural Research voi. xv, no. 12 



Peridermium pint are not complete nor detailed enough to enable one 

 to compare directly the structure of the acicolous and caulicolous aecia 

 with the structure of the aecium of Cronartium rihicola. It is evident, 

 however, that the leaf and stem types are quite similar. Study of the 

 expansive aecia of C. occidentale Hedge, Bethel, and Hunt may reveal 

 some interesting morphological variations. 



The details given for the formation of the multilayered peridium are 

 apparently the first published record of the origin of this structure. 

 Emphasis should perhaps also be placed on the constant and normal 

 occurrence of multinucleate cells at the base of the aecium, a phenomenon 

 which has been discussed elsewhere, by suggesting that in deep-seated 

 aecia of caulicolous Peridermia the seciospore chains may be found to 

 arise more often from these placenta-like cells than from basal cells 

 arising as a result of the fusion of only two cells in the fertile layer. 

 Although recent investigators — for example, Kurssanow (27)^have con- 

 firmed the results of Christman (4) and other writers with regard to the 

 origin of the basal cell as a result of the fusion of two adjacent fertile 

 cells, it yet remains a question whether this method is constant or 

 whether certain variations in the formation of the basal cells are to be 

 expected in deep-seated aecia. 



Ludwig and Rees {28) in a recent article report some details of the 

 structure of the uredinium of Pucciniastrum agrimoniae (Schw.) Tranz. 

 Their figure would serve very well for a figure of the young uredinium of 

 Cronartium rihicola (cf. PI. 55, B). In the description of the uredinium of 

 the latter it has been shown that the peridium is formed by the coales- 

 cence of cells which are cut off from certain cells that are analagous to 

 the basal cells of the sorus. These cells also cut off urediniospore initials 

 which then divide into urediniospores and stalk cells. In the young 

 sorus these four cells — that is, the basal cell, the stalk cell, the uredinio- 

 spore, and the peridial cell — form v/hat looks like a chain of cells. As the 

 spores and their stalks mature, the row arrangement is lost in the middle 

 of the sorus, but persists at the circumference. This fact places the con- 

 clusion of Ludwig and Rees that the urediniospores of P. agrimonice are 

 borne in chains, under suspicion. Personal investigation by the writer 

 into the structure of the uredinium in this species of Pucciniastrum shows 

 that the method of formation of the urediniospores in P. agrimonice and 

 in C. rihicola is practically identical, and that therefore the spores in the 

 uredinium of the former are not borne in chains but on stalks. In the 

 case of P. agrimoniae the stalks are sometimes quite short and the basal 

 cells from which they arise are much less conspicuous than they are in C. 

 rihicola, but these differences are not important as far as the method of 

 spore formation is concerned. The encircling bank of parenchyma-like 

 cells surrounding the uredinium in C. rihicola is not found in P. agri- 

 moniae. It is difficult to interpret Magnus's {30) figures of the uredinia 

 of the Pucciniastrum group as to the exact morphology of the cells from 



