ANGIOSPERMAE 



1 19 



Dicotyledones. 



Root. The radicle of the seed 

 generally develops into a tap-root with 

 lateral branches or into a system of 

 branched roots. Main root and 

 branches possess secondary growth 

 and are often woody. 



Stem. The fibro-vascular 

 bundles are arranged usually as a 

 cylinder within the ground tissue ; 

 hence they show a circular distribution 

 on a cross-section. In young shoots 

 or near the apex of older shoots the 

 bundles are independent of each other, 

 occurring as free strands in the ground 

 tissue, but later on, through increase 

 in size and the development of inter- 

 mediary bundles, they form a complete 

 cylinder which is covered on the outer 

 side by the epidermis and cortical 

 tissues, while its centre is filled by the 

 pith. The cambium of the bundles 

 remains active during the whole life- 

 time of the plant, at least periodically, 

 producing new phloem cells on its 

 outer side, thus increasing the bark, 

 and new xylem cells on its inner side, 

 thus increasing the wood of the stem. 

 Such bundles are termed open. 



Leaves. Often provided with 

 a petiole. The fibro-vascular bundles 

 (nerves) mostly laterally branching 

 (feather-veined). 



Flowers. Mostly 4- or 5- 

 merous, but not rarely one or all of 

 the whorls simpler by abortion. 



Seed. Food materials stored 

 either in a separate tissue (albumen, 

 endosperm), or in the cotyledons. 

 Cotyledons lateral, two. On germina- 

 tion they may develop into a pair of 

 green leaves {e.g. radish), or they may 

 shrivel up, the plumule developing 

 the first pair of leaves {e.g. bean). 



Monocotyledones. 



Root. No tap-root ; the radicle 

 of the embryo soon dies after germina- 

 tion, while numerous adventitious 

 roots originate from the base of the 

 stem. These roots are fibrous (not 

 woody) and do not increase in thick- 

 ness subsequently. 



Stem. The fibro-vascular 



bundles are irregularly distributed in 

 the ground tissue, but are generally 

 more numerous towards the circum- 

 ference of the stem. The cambium 

 of the bundles is of limited activity, 

 hence there is no subsequent increase 

 in their size. For this reason the 

 stem generally does not possess the 

 power of subsequent growth in thick- 

 ness ; in some of the larger species, 

 however, the stem increases in thick- 

 ness by the formation of new bundles 

 between the older ones, e.g. Aloe. 



Leaves. Mostly sessile. The 

 fibro-vascular bundles more or less 

 longitudinal and parallel ; in a few 

 cases with lateral branches, e.g. 

 Strelitzia. 



Flowers. Trimerous, but 

 there are a few exceptions, e.g. 

 Potamogeton. 



Seed. Mostly with albumen. 

 Embryo with one apical cotyledon, 

 which acts as a haustorial organ for 

 the absorption of the food materials 

 stored in the albumen. In some 

 orders it has no other function, but 

 in others it finally forms the first leaf 

 of the seedling-. 



