316 BOTANICAL GAZETTE. [ December, 
at which time there often begins the formation of four new 
ones, which fill up the spaces between the old ones, and thus 
the whole surface of the stem becomes covered with a peri- 
derm, and the phellogen layer becomes continuous. In other 
cases the intervening spaces are not covered by means of a 
regular wing, but the cork formation seems to occur about 
the same time under all the stomata, so that after a time the 
whole surface is covered by an irregular periderm which 
grows up nearly even with the sharply projecting wedges of 
the wings. 
Euonymus Americanus has a rind very similar in struc- 
ture to that of alatus; it has, however, bast fibers in the 
corners, but they lie below the chlorophyll-holding cells. No 
wings have been discovered on this species, but it is rather a 
Suggestive fact that on some young branches a line of cork 
growth often occurs running along the internode, neither in 
the middle between, nor exactly at, the corners of the stem, 
but close by these projecting corners. This growth never 
develops into more than a little brown ridge along under the 
green one of the corner. It is well known that Euonymus 
verrucosus has warty projections of cork, which are said to 
arise from lenticels, though at the time of their origin there 
iS nO appearance of periderm, unless the outer cylinder, 
which we have described as collenchymatic cells, be consid- 
ered periderm. 
which at first is only two layers in thickness. By means of 
these additional ceils from the epidermis the number 1s 1n- 
creased often to six or seven layers 
Biological Depariment, University of Pennsylvania. 
EXPLANATION oF PLATES XXII AND» xxv.—The first six figures 
Fepresent diagrammatically the phases of growth of the wings of Quercus 
macrocarpa. The first four represent one year’s growth, the fifth and 
—s slightly different phases of a stem of three year’s growth; @ 4, 
reak of the periderm tissue along the line of the five angles; 0 0, the 
