1900 ] LIFE HISTORY OF SILPHIUM 123 
embryo. A third cell divides transversely, its inner half com- 
pleting the dermatogen and its outer half becoming the first 
layer of the root cap. 
It was seen very early in the course of the investigation that 
Silphium did not follow the process found in Capsella, and 
described by Fleischer for Helianthus. Nor could the stages 
found be made to agree with Schwere’s Taraxacum embryos. The 
mode of origin of periblem and dermatogen terminals resembles 
more nearly the process as found by Hanstein in CEnothera, the 
greatest difference being in the origin of the periblem terminal. 
This, instead of being cut out as a lenticular cell from the upper 
side of the hypophysis cell, is apparently formed by the inter- 
section of three walls, inclined so as to meet the basal wall of 
tierce. Figs. 86 and 88 partially illustrate this process. The first 
of these three walls may at first appear to be longitudinal, as in 
Jig. 1, but it is plainly oblique in fig. 86. In fig. 88 the second 
oblique wall is shown, and a third nucleus, in the tier below the 
periblem terminal, but in another focus, gives proof of the pres- 
ence of a third dermatogen terminal. 
In fig. 89 the periblem terminal has divided by probably two 
longitudinal walls, giving a plate of four cells. In fig. go, by 
a shifting of the cells, the periblem terminals have been drawn 
still farther into the pear-shaped body of the embryo. Another 
wall in the dermatogen terminals gives three cells in section, the 
middle one being quite broad. In jig. 97 the two lateral derma- 
togen terminals have split to produce a layer of the cap; and 
the presence and direction of the spindle in the middle cell fur- 
nishes conclusive proof that the root cap arises by the splitting 
of the dermatogen. Fig. 92 shows a portion of a much older 
embryo, seen entire in fig. 92, a. The relations of the primary 
tissues are the same as in jig. 91. The boundaries between ple- 
rome and periblem are made heavy, and the epidermal cells are 
drawn with nuclei. The greater thickness of the cap at the end 
of the embryo is caused by the splitting of the layers of the cap 
itself, as can be seen clearly in several places. The apparent 
diminution in the size of the cells is almost entirely due to the 
