MORPHOLOGY OF HIGHER PLANTS. 



299 



The vegetative organs comprise the root and shoot, the latter 

 being usually differentiated into shoot axis or stem, and leaves. 

 The usual type of shoot is one which bears leaves and is exposed 

 to the light. The work of carbon dioxide assimilation (photosyn- 

 thesis) being carried on for the most part by the leaves, the axis 

 is sometimes spoken of as the " assimilation shoot." 



FIG. 161. A, advanced stage of germination of the common garden pea (Pisum sa- 

 tivum) showing growing point of root protected by root-cap (p); root branches or second- 

 ary roots (rb); hypocotyl (he); epicotyl or stem above the cotyledons (ec) ; cotyledons 

 (one in view) (c). B, plantlet of white or yellow mustard (Sinapis alba) showing copious 

 development of root-hairs (h). 



I. OUTER MORPHOLOGY OF THE ROOT. 



THE ROOT, or descending axis of the plant, normally pene- 

 trates the soil, absorbing inorganic substances in solution and act- 

 ing as an anchor and support for the shoot. True roots are found 

 only among plants having a vascular system, as the Spermophytes 

 and the higher Pteridophytes, although, on the other hand, some 

 of the higher plants do not possess them, as certain of the sapro- 

 phytic orchids and some of the aquatic plants as Utricularia, 



