235 
to the question how far this anatomical difference, that is, the 
presence or absence of the dorder in the libriform tissue, coincides 
with the morphological characteristics which decide the limits of 
genera, families and groups in our present system of classifica- 
tion. 
Specimens from nearly all the genera of the large and most 
important dicotyledonous families were studied and compared in 
reference to this question. Some few of these families contain 
only two or three genera with woody tissue; of others only a few 
species were available, but the greater number of the families 
given in the following list were exhaustively examined. 
With this examination we begin by comparing the genera of 
the different families, as there is no question in regard to the 
similarity of anatomical structure, in this respect, between the 
different species of the same genus. ; 
Genera from sixty-one principal and six sub-families were 
examined with the results shown in the following tables; the 
sub-families are given here separately owing partly to the large 
number of genera some contain, and partly on account of certain 
differences in structure which incline botanists to regard them as 
distinct families. 
FAMILIES WHOSE LIBRIFORM CONTAINS ONLY SIMPLE PoREs. 
Anacardiacez. Corylacez. Polemoniacee. 
Araliaceze. Euphorbiacee. Plumbaginez. 
Acanthacez. Ebenacez. Primulacez. 
Anonacez. Juglandacez. Rutacez. 
Acerinez. Labiate. Rhamneze. 
Ampelidez. Lobeliacez. Salicinez. 
Borragineze. Lauracez. Selaginez. 
Bignoniacez. Moree. Ulmacee. 
Betulacez. Myrsinez. Umbelliferz. 
Berberidez. Meliacez. Verbenacez. 
Composite. Papilionaceze. Valerianacez. 
, FAMILIES WHOSE LiIBRIFORM CONTAINS ONLY BORDERED Pores. 
Apocynacez. Gordeniacez. 
Asclepiadez. Magnoliaceze, Sus-FaMILigs. 
Cornacez. Proteacez. 
Dipsacez. Platanez. Dryadez. 
Epacridez. Rhodoracez. Pomez. 
Ericacez. Staphylacee. Rosez. 
Empetracez, Vacciniex. 
Styracez. 
