CHAPTER XIII. 



THE LOWER DICOTYLEDONS. 



318. The Bentham-Hooker System, The classification 

 of the Lower Dicotyledons differs considerably in different 

 systems which have been proposed. The Higher Dicotyledons 

 (G-ainopetalae) form a more sharply defined series, and their 

 classification varies in detail only in different schemes. 



In the Bentham-Hooker System the Lower Dicotyledons 

 are divided into (1) " Incompletae," in which the flowers 

 have a simple and usually sepaloid perianth, or none, and 

 are often unisexual, and (2) " Folypetalae," in which the 

 perianth is double, the inner whorl being petaloid and free 

 (polypetalous) . But the " Incompletae ' ' include many Orders 

 which are clearly related to certain Orders of " Polypetalae," 

 though sometimes it is difficult to say whether the " Incom- 

 pletae" are primitive (i.e. on the upgrade of evolution) or 

 reduced (i.e. on the downgrade). 



The "Polypetalae" are divided, in this system, into three 

 groups: (1) " Thalamiflorae," with strictly hypogynous 

 flowers ; (2) ' Disciflorae," hypogynous but with a " disc " 

 (forming a ring or cushion spread over the base of the calyx- 

 tube, or fused with base of ovary, or represented by a series 

 of separate glands) on which the stamens are inserted; 

 (3) " Calyciflorae," with perigynous or epigynous flowers. 



319. The Engler-Prantl System, adopted in the great German 

 encyclopaedia Die natiirlichen Pflanzenfamilien, does away with many 

 of the defects and artificialities of the Bentham-Hooker and other 

 systems. The Gamopetalae remain much the same, on the whole, but 

 the "Incompletae" are placed with the "Polypetalae" in a single 

 series distinguished by having a relatively simple perianth. We shall 

 study in detail some typical Orders, not adhering rigidly, however, to 

 the sequence set out in the Engler-Prantl scheme. 



