THE DIPFEEENTIATION OF THE PLANT-BODY 27 



The same tissues serve for transport in the Monocotyle- 

 dons, and in the Vascular Cryptogams, though the mode of 

 arrangement of the elements is altogether different from 

 that of the Dicotyledons. 



In those vascular plants which live in water, and parti- 

 cularly in those which are totally submerged, there is no 



need for so elaborate a transport 

 system, as water can be readily 

 absorbed by the general surface. 

 We find two modifications of 

 structure in such plants ; the 

 epidermis is hardly at all cuti- 



FIG. 27. DIAGRAM OF THE COURSE 

 OF THE VASCULAR BUNDLES IN 

 AN HERBACEOUS DIOOTYLEDO- 

 NOUS PLANT. 



FIG. 28. DISTRIBUTION OF THE 

 VASCULAR BUNDLES OR VEINS 

 IN A FOLIAGE LEAP. 



cularised, so that water can pass from the exterior into its 

 cells ; while the vascular bundles are comparatively feebly 

 developed, the woody part of them being particularly small. 

 The third requirement of a plant of considerable mass, 

 especially if it has a terrestrial habitat, we have seen to be 

 a power of resisting such external forces as would lead to 

 its uprooting, which must be combined with a considerable 

 degree of flexibility, at any rate at the extremities of the 

 body. This combination of rigidity and flexibility has been 

 secured in various ways, varieties of both the form and 

 the structure of the plant being concerned in it. In the 

 simplest plants but little differentiation of the body is 



