Subdivision i 
DICOTYLEDONES (see Volume I) 
Dicotyledones Jussieu Gen. PI. lxxi et 70 (1789); Ascherson und Graebner Syn. iv, 1 (1908); 
Dicotyledoneae DC. Syst. i, 122 et 123 (1818); Prodr. i, 1 (1824); Engler Syll. 92 (1892) including Chalazogamae 
p. 64. 
Cotyledons 2, rarely 1 or more than 2 (or apparently 1 or more than 2) or absent, lateral. Primary 
root usually persistent, except in geophilous forms. Plumule terminal. Leaves often consisting of 
stipules, petiole, and lamina, but many stages of reduction and many modifications occur ; basal sheath 
usually absent and if present usually imperfect ; laminae usually either pinnately veined or palmately 
veined, smaller veins reticulate ; veins more or less obscured in succulent forms. Perianth mono- 
chlamydeous or dichlamydeous or rarely absent ; segments usually cyclic (i.e., whorled), rarely spirally 
arranged ; sepals usually 4 or 5, less commonly 3, rarely 1 or 2 or more than 5 ; petals usually as 
many as the sepals. 
It is important to bear in mind that there is scarcely a single group of plants whose characters are constant. No 
matter which character or combination of characters be emphasised, plants can be found which refuse to accom- 
modate themselves to the groups made by systematists. Consequently, be these groups constructed ever so well, 
the student soon perceives that there is no easy method of determining in which group a critical plant must be 
placed. This indeed is only what is to be expected if the doctrine of evolution is true. The only general rule 
which can be safely laid down is that the totality of the characters of a plant and not any single character or com- 
bination of characters must be taken into consideration in determining its systematic position. 
Dicotyledons with more than 2 or apparently more than 2 cotyledons occur, e.g., in Acer. Dicotyledons which 
have or apparently have only 1 cotyledon occur, e.g., in Carurn , Chaerophyllum , Corydalis , Cyclamen, Eranthis , 
Ranunculus. Dicotyledons which are destitute of cotyledons occur, e.g., in Cuscuta, Orobanche, Viscum. 
Although the subdivision Dicotyledones as now understood dates from de Jussieu ( toe . cit.), yet the name had been 
used previously by Ray {Hist. Plant. (1686 — 88)), Hallier (Enum. Helv. 33 et 321 (1742)), Linnaeus {Phil. Bot. 102 
(1751)), and Gaertner {Fruct. i, clxxix (1788), ii, xliv (1789)); and the concept had been foreshadowed in 1570 
by de L’Obel {Stirp. Adv.). It was Ray {loc. cit.) who first realised the importance of the characters of the 
cotyledons in classification, although the influence of the pre-Raian botanists who laid stress on mere plant- 
form in classification prevented a rigorous and logical application of his discovery. 
In Engler’s arrangement {Syll. editions 1—7), the Monocotyledones are placed before the Dicotyledones ; but the 
general opinion among botanists at the present time is that although the latter have reached a higher state of develop- 
ment than the former, yet the former originally evolved from the latter ; and in deference to the widespread nature and 
probable truth of this view, the Dicotyledones are in the present work taken before the Monocotyledones. In adopting 
this plan we are following Wettstein {Handb. Syst. Bot. ed. 2 ( 1 9 1 1 )) among modern systematists, and Bentham and 
Hooker {Gen. Plant. 1862 — 1883) and De Candolle {op. cit.) among botanists of an earlier date. 
Classes of Dicotyledones 
Class 1. Archichlamydeae (p. 2). Perianth (1) monochlamydeous in the lower forms, 
(2) dichlamydeous in the higher forms, or monochlamydeous by reduction and then with allied 
forms dichlamydeous, (3) absent and then present in allied monochlamydeous or dichlamydeous 
forms. Outer whorl of perianth or calyx either polysepalous or gamosepalous. Inner whorl of 
perianth or corolla usually polypetalous, when gamopetalous, allied forms are polysepalous. 
Gamopetalous forms occur, e.g., in Cotyledon. Cf. also Portulacaceae. 
Class 2. Metachlamydeae or Gamopetalae. Perianth usually dichlamydeous, rarely mono- 
chlamydeous or apetalous, and then with dichlamydeous forms in allied genera ; usually gamopetalous, 
rarely polypetalous and then with gamopetalous forms in allied genera or families. 
Polypetalous forms occur, e.g., in Pyrola, Monotropa. Many genera, especially in Ericaceae , Plumbaginaceae, and 
Primulaceae are almost or even quite polypetalous. Monochlamydeous forms occur, e.g., in Glaux. Achlamydeous 
forms occur, e.g., in Fraxinus. 
M. II. 
I 
