Weeds of South Africa. 



319 



In germination the cotyledons may come above tlie ground, in 

 which case the germination is said to be epigean, e.g. the Malta 

 Thistle (Centaurea meliteiisis) , etc. ; when they remain below the 

 ground the germination is hypogean, e.g. broad bean seeds or pea 

 seeds, etc. (See figs. 1 and 2.) 



The Root is one of the four important organs of a plant. It 

 increases in length by the elongation of the growing point, which is 

 situated a short distance behind the extreme tip. Not far from the 

 root apex are the root hairs, which are the channels through which 

 the water of the soil with mineral salts in solution enters the root. 



There are different kinds of roots, e.g. : — 



.4 fihrovs root, one in which the rootlets are in the form of 

 fibres, such as the Mexican Marigold (Tagetes minuta), etc. 

 (See fig. 3.) 



A tap root is an elongated much thickened main root, e.g. the 

 Spear Thistle (Cnicus lanceolatus) . (See fig. 4.) 



Fig. 7. — Stems showins: opposite and alternate leaves. 



In the Lucerne Dodder (Cv scuta spp.), which is a parasite, peg- 

 like out-growths called haustoria are produced from the stem which 

 penetrate the tissues of the host and absorb food. These haustoria 

 are regarded as modified roots. (See fig. 6.) 



The Stem is the axis of a plant usually above the ground. It is 

 divided into nodes and internodes; the leaves arise at the nodes, and 

 the portions of the stem between the nodes are the internodes. Buds 

 are also produced on the stem in the axils of the leaves. (See fig. 7.) 



A rhizoTne is a creeping underground stem which sends out roots 

 from its lower surface, and stems and leaves from its upper surface, 

 and so forms new plants, e.g. the Canada Thistle (Cnicvs arvensis). 

 (See fig. 5.) 



