1900] LIFE HISTORY OF SILPHIUM 133 
Fic. 90 S. trifoliatum. Two concentric layers of cells in plerome of lower 
octants and of tierc ; periblem and dermatogen terminals almost as in fig. 89. 
Fic. 91. S. integrifolium. Anticlinal divisions in periblem-terminals ; 
periclinal walls in lateral dematogen-terminals (de), and the spindle in mid- 
dle one show formation of first layer of root cap. 
FiG. 92. S. integrifolium. Portion of a much older embryo, outlined in 
Jfig.92,a; nuclei in dermatogen cells only; periblem and plerome ee 
rated by heey line; outer layers of root cap irregular. 
