THE MONOCOTYLEDONES 



2031 



n 



B 



Fig. 1970. — Iris uu^uiciilaris. A, Flower in longitudinal 

 section with narrow erect styles. B, Downward con- 

 tinuation of the tube to the ovary. 



The seed possesses copious endosperm in which is enclosed a small 

 embryo. 



The family is widely distributed in temperate and tropical regions and 

 includes some sixty genera and over 800 species. 



Morphologically the chief interest in the family centres in its organs of 

 vegetative propagation. In the genus Iris the majority of the species grow 

 by sympodial rhizomes which are thick and fleshy and develop only just 

 below the surface of the soil. In the Xiphion section, as illustrated by 

 /. xiphiiim itself, a bulb is produced, which bears a stem carrying a few 

 cauline leaves. Corms, derived from the lowermost internode of the stem, 

 are the most common type of rootstock. These corms arise towards the 

 end of the first year in the life of the seedling and thereafter the primary 

 root disappears and is replaced by adventitious roots borne on the corm. 



Only in the genera Artstea, Witsenia and Klattia is a shrubby habit 

 developed. In Witsenia the stem is branched repeatedly, producing a shrub 

 about 4 ft. high. A curious type of secondary thickening has been described 

 in Aristea corymbosa where a cambium is formed in the pericycle which 

 gives rise internally to additional complete vascular bundles embedded 

 in ground tissue while on the outside it produces secondary cortex. At the 

 same time a cork cambium, developed in the cortex, produces external 

 cork and some internal secondary cortex. 

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