28 SCIENCE PRIMERS. [vii. 



plumule and radicle of the pea to its cotyledons. 

 The plantlet here feeds on the flour of which we make 

 bread, just as the pea plantlet fed on the part of the 

 pea which we eat. 



The radicle of the wheat does not elongate upon 

 germination, as that of the pea and mustard did, but 

 rootlets grow out from it with sheaths at their base. 



39. These great differences between the cotyledons, 

 the growth of the root, and the mode of germination 

 of the pea (or mustard) and of the wheat, are most 

 important, being characteristic of the two great divi- 

 sions (classes) of flowering plants, called Dicotyle- 

 dons (plants with two cotyledons or seed-leaves) and 

 Monocotyledons (plants with one cotyledon or 

 seed-leaf), which divisions are further to be recognized 

 by other characters hereafter to be described. 



VII. THE ROOT. 



40. The root is formed by one or more pro- 

 longations of the radicle of the embryo (Sect. 36). 

 Its uses to the plant are, to fix it to the ground, to 

 absorb nourishment from the latter, and sometimes 

 to store up and retain nourishment during winter for 

 the food of the plant during its growth in the following 

 spring. 



41.. Roots are known from stems by their growing 

 downwards from the plantlet (Sect. 36), and usually 

 afterwards avoiding the light ; by their not, or very 

 rarely, bearing buds; and by their structure and mode 

 of growth. 



42. When only a single prolongation of the radicle 

 is formed this is called a tap-root. This bears at its 



