494 



BOTANY OF THE LIVING PLANT 



ous Flow 



base, and parallel venation ; but the Dioscoreaceae are exceptional in having 

 broad reticulate leaves. 



The flowers are constructed on a type which may be accepted as a general 

 underlying plan for Monocotyledons, being com- 

 posed of five alternating whorls of parts. The 

 number of parts in each whorl is commonly 

 three ; but other numbers may be found, such as 

 two (Maianthemum), or four, or even five (Paris, 

 Aspidistra}. The floral formula is P. n + n, And. 

 n + n, Gyn. (n), and the floral diagram as in 

 Fig. 397. The more primitive Liliiflorae have 

 hypogynous flowers, but they are epigynous in 

 the Amaryllidaceae and Iridaceae, a condition 

 regarded as later and derivative. The ovary has 

 one loculus for each carpel, and the anatropous 

 ovules are seated on their incurved margins, which 

 are fused to form an axile placenta (Fig. 399). The 

 flowers are usually of large size, and are often 

 conspicuous by colour and scent (Lily, Tulip) . They show steps of progressive 

 fitness for the nursing of the ovules, by various degrees of fusion of the 

 carpels, and of sinking of the ovary from the superior position of the 

 Liliaceae to the inferior of the Amaryllidaceae and 

 Iridaceae. Progressive steps may also be traced in per- 

 fection of the pollination-mechanism. 



Family : LILIACEAE. Example : THE TULIP. 



(i) The Tulip plant (Tulipa gesneriana) at the flowering 

 period consists of the underground bulb, bearing roots 

 downwards from the margin of the disc-like stem, upon 

 which the storage-scales of the bulb are seated. From its 

 apex rises an elongated stem bearing a few foliage leaves, 

 and a single terminal flower which is radially symmetrical. 

 Provision for the next season is made by one or more 

 buds in the axils of the bulb-scales, which grow into new 

 bulbs, and each may produce a flower. Compare bulb of 

 Hyacinth (Fig. 125, p. 166). The analysis of the flower is 

 as follows : 



Perianth segments 3 + 3, polyphyllous, inferior. 

 Androecium stamens 3 + 3, free, hypogynous. 

 Gynoecium. carpels 3, syncarpous, superior. Stigma 

 three-lobed, sessile. Ovary trilocular. Placentation 

 axile. Ovules numerous, anatropous (Figs. 398, 399). 

 The floral diagram (Fig. 397) shows the regular alterna- 

 tion of the successive whorls of three parts. As those of 

 each whorl are all of equal size, and excepting the carpels all 

 separate from one another, the Tulip may be held as a relatively primitive 

 type of Liliaceous flower. But the syncarpous state here seen is probably 

 not the most primitive. In Colchicum, with its Crocus-like habit, the carpels 



Ov 



FIG. 398. 



Su 



iperior gynoecium 

 of Lilium, showing re- 

 lative position of ovary 

 (ov), style (sty), and 

 stigma (stig). 



