DICOTYLEDONES 413 



For a detailed account of these, the student may refer to any of the 

 special works on the subject. 



Many special devices for distributing the seeds, either through the 

 agency of the wind, or by bursting of elastic capsules, or by animals, 

 have been developed. Such are the numerous edible fruits, and the 

 winged seeds and fruits, as well as the adhesive ones, so often 

 encountered. 



Classification of Dicotyledons 



The classification of the Dicotyledons is in a very unsettled condi- 

 tion, and the one adopted here 1 can only be considered a provisional 

 one. They are commonly divided into two series, Archichlamydese 

 (Apetalae, Choripetalae) and the Metachlamydese (Sympetalae). In 

 view of recent studies upon the Apetalse, it seems best to recognize 

 these as a distinct series, so that we may recognize three series (sub- 

 classes of Engler), of equal rank, Apetalae, Choripetalse, and Syrnpe- 

 talse (Archichlaniydeae, Mesachlamydese, Metachlamydese). 



SERIES I. APETAL.E (ARCHTCHLAMYDE^E) 



The Apetalae comprise several orders of Dicotyledons which are 

 very different from the typical Choripetalse, and are probably the 

 most primitive members of the group. Some of them, especially the 

 Piperales, show certain resemblances to some of the simple Mono- 

 cotyledons, and may be remotely related to them. For the most part, 

 they show but little affinity with the higher Dicotyledons, and should 

 probably be removed from their association with the Choripetalae. 



The flowers of the Apetalaa are of very simple structure, and often 

 diclinous (e.g. Morus, Populus, Fagus), the plants being either monoe- 

 cious (Quercus) or dioecious (Morus). The flowers may be quite 

 destitute of envelopes (Peperomia, Saururus, Salix), or there may be 

 a simple perianth, of usually inconspicuous scalelike leaves. In 

 some Polygonales, the perianth is petaloid, but there is some ques- 

 tion whether these are not more properly included in the Chori- 

 petalae. In no case is the perianth differentiated into calyx and 

 corolla. 



Many of the Apetalas are shrubs or trees, and some of the most 

 important forest trees, especially in the temperate regions, belong to 

 the Apetalse. Among these are the Oaks, Beeches, Elms, Walnuts, 

 Hickories, Willows, Poplars, Birches. 



1 The classification adopted here is with very slight modifications that of Engler, 

 " Uebersicht iiber Unterabteilungen, Reihen, Unterreihen und Familien der Embryo- 

 phyten Siphonogamen," in Die Natiirlichen Pflanzenfamilien, 2-4 Theil, Nachtrag, 

 1897. 



