'28 METASPERMAE OF THE MINNESOTA VALLEY. 



Luerssen (43) 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). ArcUichlamydeae: Perianth wanting or made up of 

 incoherent leaves owing to the failure of parts in the same 

 foliar circle to undergo fusions. 



(b). Metacklamydeae: 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 a condition 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, (1882X 

 (44) Van Tieghem: Traite de Botan., Vol. II, (1891) . 



