24 BOTANICAL GAZETTE [july 



however, that two or more layers of peridial cells are apparently 

 formed regularly in certain species of Peridermium (3). When the 

 peridium is completed over the entire outer surface of the spore 

 mass, its subsequent enlargement is accomplished entirely by the 

 basipetal addition of cells to its lateral walls from the peripheral 

 basal cells. 



The cytoplasm of the mature peridial cell is vacuolate and the 

 nuclei are smaller and more compact than those of the aecidiospore. 

 It is difficult to be sure whether they have decreased in size with 

 the metamorphosis of the cell or whether they have not been com- 

 pletely reconstructed from the preceding mitosis- The latter expla- 

 nation seems more probable and is supported by some observations 

 that are not, however, conclusive. In size and general appearance 

 they resemble the nuclei of the intercalary cells. They do not 

 become disorganized; the chromatin masses and nucleoles stain 

 deeply and are sharp and clean-cut. The walls stain with the 

 orange, and a properly stained peridial cell is easily distinguished 

 from an aecidiospore by the thickness of the wall as well as by the 

 comparative emptiness of the cell and smallness of the nuclei. The 

 outer side of the wall, the one next the pseudoparenchyma, is 

 thicker than the inner or lateral sides (fig. 15). This was true to 

 some extent of all of the forms I have studied. The nuclei are often 

 located near the thickest part of the wall. The process of wall- 

 thickening accompanies the decrease in the density of the cytoplasm, 

 and the natural assumption is that the thickening is produced by 

 the deposition of substances from the cytoplasm. No stratification 

 appears in the walls. They may be variously sculptured, however, 

 and the outer portion of the wall is usually marked by transverse 

 striae. 



The origin of the peridium is more easily followed in the broad 

 cup of Ur. Caladii than in any of the other forms. The greater 

 part of the peridium that is formed here before the rupture of the 

 epidermis originates from interior spore chains. This is apparent 

 even in mature cups, as shown in text fig. 5, which is a semi- 

 diagrammatic representation of a stage before the rupture of the 

 epidermis. Of the peridial cells shown here, 14 are in all proba- 

 bility of interior chain origin. There are about 29 interior chains. 



