RICHARDS. — DEVELOPMENT OF ^CIDIA. 267 



which give rise to the basidia. At this poiut there is apparently 

 some difference in the development of different species, and even in 

 the tBcidia of the same species. In the tecidia on Peltandra and 

 Iloustonia, at least among the smaller ones, the basidia arise with but 

 little branching on the part of the fertile hypha, while in the form 

 described on Ranunculus the fertile hypha seems to branch to some 

 extent, and in the aecidiura on Amemone it forms apparently an 

 extended growtli before giving rise to the hyraeniura. It is probable 

 that in some cases, particularly in the larger iecidia, more than one 

 fertile hypha takes part in the formation of the hymenium. 



In the formation of the spores, there is first formed what may 

 be called the spore mother cell, from which by division is formed 

 the spore itself and the small interstitial cell, in the manner previously 

 described. Plowright * speaks of the spores as being formed in a 

 mother cell, and that by subsequent growth and thickening of the 

 walls the spore and the mother cell fuse together. Such, however, 

 can hardly be considered the state of affairs, for the intercalary cell 

 is plainly cut off in the manner described by Rosen and also given 

 in this paper. 



Regarding the peridium, the view advanced here is probably more 

 different from the generally accepted idea than any other particular 

 mentioned in this paper. Almost everywhere one finds the statement 

 that the peridium originates along the sides and "arches over" the 

 hymenium. De Bary has said that the cells of the peridium do not 

 possess intercalary cells, but this is hardly the case in the tecidium 

 herein desci'ibed on Sambucus, although in other cases the thickening 

 of the wall might begin before it was time for the intercalary cell to 

 be formed, in which case its production might be interrupted. It 

 might be objected that the union of the terminal cells with the pe- 

 ripheral spore chains to form the peridium is hard to account for, but 

 when one considers the condition of affairs in the young gecidium it 

 is not so difficult to understand. The walls of the young peridial 

 cells are very delicate, and, being under a relatively considerable 

 pressure, are literally forced together. It is true that in their subse- 

 quent development the peridial cells on the side increase mainly in 

 length, while the peridial cells on the top of the secidium increase 

 in all directions ; but that is hardly an unsurmountable objection. It 

 may be that it is the pressure under which the cells of the peridium 

 are formed which induces the excessive thickening of the wall. 



* Loc. cit., p. 22. 



