420 
IRIS 
upper surface is the stigma. Bees entering the fir. to get the honey 
secreted by the ovary rub off their load of pollen upon the stigma ; 
going farther in they get a fresh supply of pollen; and when they 
come out close the stigma flap, which prevents self-fertilisation (cf. 
Viola). The flat seeds are suited to wind-distribution. 
The dried rhizome of 7 . florentina, L. smells like violets, it is 
known as Orris root, and is largely used in perfumery; ‘essence of 
violets ’ is made from it. 
Isatis Tourn. ex Linn. Cruciferae (n. 8). 50 sp. Medit., Eur., As. 7 . 
tinctoria L. is the woad, largely used as a dye before the introduc- 
tion of indigo. It is prepared by grinding the leaves to a paste 
and fermenting them. 
Isnardia Linn. = Ludwigia Linn. 
Isoetaceae. Lycopodinae (Heterosporous). Only genus Isoetes (q.v.). 
Isoetes Linn. Isoetaceae. 50 sp. temp, and trop. 7 . lacustris L. is 
the quill- wort of Brit, lakes, and 7 . echinospora Dur. is also found. 
Most sp. are aquatics with short stout rhizomes and awl-shaped 
leaves, the habit being very like that of Littorella, with which I. is 
frequently confused. The stem grows in thickness, but very slowly. 
The leaves spread out at the base and sheath the stem. There are a 
number of roots, which branch dichotomously. Above the base of 
each leaf, on the inner side, is a large sporangium sunk in the tissue. 
The outer leaves have micro- the inner mega- sporangia, whilst the 
innermost leaves of all are usually small and not sporangiferous. 
The sporangia are imperfectly chambered up by strands of tissue 
( trabeculae ) running across them from front to back. The germination 
of the spores and the development of the embryo resemble the corre- 
sponding processes in Selaginella. 
I. is frequently placed with the Eusporangiate Filicineae (see 
Campbell, Mosses and Ferns). It differs so much from all other 
Pteridophyta that the determination of its relationships is a matter of 
great difficulty. 
Isolepis R. Br. = Scirpus Linn. 
Isoloma Dene. ( Kohleria Regel). Gesneraceae (11). 40 sp. trop. Am. 
Several sp. form runners above ground, thickly covered with scaly leaves. 
Isonandra Wight. Sapotaceae (1). 6 sp. Ceylon to Sumatra. [ 7 . 
Gntta Hook. = Dichopsis Gutta .] 
Isopogon R. Br. Proteaceae (1). 29 sp. Austr. 
Isopyrum Linn. Ranunculaceae (2). 17 sp. temp. As. 
Isotoma Lindl. Campanulaceae (in). 6 sp. Austr., 1 W. Ind., 1 
Society Is. 
Ixia Linn. Iridaceae (ill). 25 sp. S. Afr. 
Ixiolirion Fisch. Amaryllidaceae (1). 2 sp. W. As. 
Ixora Linn. Rubiaceae (11. 14). 100 sp. trop. The fir. is commonly 
red with a long narrow tube, and probably, therefore, butterfly- 
visited (p. 91). The mechanism is like that of Campanula. 
