256 THE SEED PLANTS I FORMS AND LIFE HISTORIES 



(annual plants), or the aerial shoots alone may die off, 

 leaving persistent underground shoots (perennial plants). 

 The underground shoot may be woody and persist 

 indefinitely, constantly increasing in thickness as 

 well as in length like a woody subaerial shoot, or while 

 growing at the apex from year to year it may con- 

 tinuously die off behind. In this chapter we shall 

 consider some of the leading herbaceous types of seed 

 plant body. 



Erect Herbaceous Annual. This is the simplest 

 type of herbaceous plant, but is not to be considered 

 the most primitive, the form from which the other 

 types are derived. On the contrary, it is believed by 

 botanists, on very good grounds, that woody perennial 

 plants are the most primitive forms of the higher plants, 

 and that the herbaceous, and finally the annual plants, 

 have been derived from these. 



The body of an annual (Fig. 40, A) consists of a 

 descending portion, the primary root or taproot, and its 

 branches. These penetrate the soil, fix the plant, and 

 absorb water and inorganic salts from the soil ; and the 

 green shoot, which ascends into the air and consists of 

 the axes (stems) and typically flat plate-like organs borne 

 on them the foliage leaves. 



The first leaves borne by the stem those nearest 

 the root are typically a pair already formed on the 

 embryo in the seed, and generally simple in form : 

 these are called the cotyledons. The part of the stem 

 between the cotyledons and the top of the root is 

 called the hypocotyl. In the young seedling plant 



FIG. 40. A, diagram of annual plant : t.r., taproot; hyp., hypocotyl; 

 cot., cotyledouns ; /, foliage leaf ; ax., axillary bud ; t.b., terminal bud ; 

 fl.b., flower bud. B, part of underground stem (rhizome) of Cora" 

 root (Dentaria) showing fleshy scale leaves (sc.l.) of adventitiou 

 roots (r), lateral bud (Lb.), aerial shoot (a.s.), arisen from the 



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