CYCADACE^ — HYDEOCHAEIDACE^. 601 



mucilage. From the stems of Cycas revoluta (fig. 519, p. 292) and 

 C. circinalis a kind of Sago is made. A clear insipid mucilage also 

 exudes from them, which hardens into a transparent gum resemb- 

 ling tragacanth. Bion edule yields a kind of arrow-root in Mexico. 

 Zamia pumila, and other species in the West Indies, supply an 

 amylaceous matter, which has been sold as Arrow-root. The Bread- 

 tree is a name applied by the Hottentots to various species of 

 Uncephalartos. 



Class II. — Monoootylbdones, Jiiss. Endogen^, DO. Endogens and 

 DiOTTOQENS, Zdndl. Amphibrta, ^ndl. 



In this great class the plants have a cellular and vascular system, 

 the latter consisting partly of elastic spiral vessels (fig. 53, p. 17). 

 The woody stem (as in Palms, fig. 134, 1, p. 68) is usually more or 

 less cylindrical, simple, and unbranched. There is no true separ- 

 a,ble bark, no concentric zones, and no true pith (figs. 131, 132, p. 

 65). The wood is endogenous, i.e. increases by additions, which first 

 tend towards the centre, and then curve outwards in an interlacing 

 manner (fig. 133, 2, p. 66) towards the circumference, where much 

 hard ligneous matter is deposited, so as to make the exterior the 

 hardest part. The development of the stem usually takes place by a 

 single central and terminal bud ; occasionally lateral buds are pro- 

 duced (fig. 134, 2, p. 68), and at times the stem is hoUow. The 

 leaves are usually parallel-veined (figs. 150, p. 83 ; 188, p. 90 ; 210, 

 p. 99). The parts of the flower are arranged in a ternary manner 

 (fig. 637, p. 365), and they are often petaloid (fig. 284, p. 92), 

 sometimes scaly or glumaceous. The ovules are contained in an 

 ovary, and are fertilised by the application of the pollen to the 

 stigma. The embryo has one cotyledon (fig. 600, p. 336), and the 

 germination is endorhizal (fig. 626, p. 355). 



Sub-class I. — Petaloide^. 



Flowers having usually a perianth consisting either of vertioU- 

 late leaves, which may sometimes be separated into calyx and corolla, 

 and are often coloured (petaloid), or of a few whorled scales. Occa- 

 sionally the perianth is abortive. 



a. EpiG-YNA — Ovary inferior, Flowers usually herma'phrodite. 



Order 185. — Hydeoohaeidacb^, the Frog-bit Family. (Mono- 

 Epigyn.) Flowers spathaceous, unisexual, rarely § . Perianth with 

 a 6-partite limb, the 3 outer segments herbaceous, and equivalent 

 to the calyx, the 3 inner petaloid, and equivalent to the corolla. Sta- 

 mens definite or indefinite, epigynous. Ovary inferior, 1- or many- 



