28 METASPERMAE OF THE MINNESOTA VALLEY. 
Luerssen (48) or, not so naturally, by Van Tieghem (44). The 
Dicotyledones however admit of arrangement in two distinct 
divisions, based upon the morphological characters of the 
perianth. These are as follows: 
(a). Archichlamydeae: Perianth wanting or made up of 
incoherent leaves owing to the failure of parts in the same 
foliar circle to undergo fusions. 
(b). Metachlamydeae: Perianth exhibiting fusions between 
parts of the same foliar order or indicating, by accessory 
characters, an ancestral line in which such fusions must have 
taken place. 
Under the classification above worked out the plants of the 
following list are arranged. It must be remembered that the 
families follow each other in precisely the order laid down in 
the monographers’ work, in Engler and Prantl. Thus it is 
believed, a system as natural as available has been adopted, 
and the arrangement of genera and species is made to conform 
so far as may be practicable to the general order. 
It is not improbable that the epoch-marking work of Engler 
and Prantl may be translated into English, but even if it is not 
it must for at least a decade stand as the highest and most 
generally accepted authority. And it is for this reason that I 
have preferred to follow its arrangement rather than the 
Benthamian which is steadily and irrevocably losing ground. 
Some citations of important literature not referred to in the 
body of the above discussion, are here added to indicate to 
students where to look for the memoirs and volumes which 
have done so much to bring to light the four-fold complexity of 
our common higher plants. It will be seen from a considera- 
tion of the metaspermic characters adduced above that what we 
call an oak, the Quercus macrocarpa. for example, is not an indi- 
vidual like an animal, but a group of four individuals of which 
one only is vegetatively important while the other three, com- 
prising both the sexual plants and one of the two sexless plants, 
are reduced into acondition of dependence which permits them, 
in ordinary parlance and in many treatises, to be discussed as 
organs. This condition might easily arise as a result of high 
differentiation and polymorphism and something like it, on a 
much simpler scale, is seen in animals like the copepods, in 
certain species of which the male is very much smaller than the 
female and lives parasitically upon the body of the larger crus- 
(43). Luerssen: Medicin.-Pharmac. Bot., Vol. I, (1882), 
(44) Van Tieghem: Traité de Botan., Vol. IL, (1891). 
