Ch. IV, 10] FOLIAGE-BEARING STEMS 



187 



living stems for their soil water, the step would seem easy for 

 roots ; and thus has probably originated the half-parasitic 

 habit represented in the Mistletoe. Thence it is only a 

 short step further to a connection with the food supplj' of 

 the host plant, and a completely parasitic habit. It is prob- 

 able that the parasitism of the flowering plants has mostly 

 originated in tliis way. 



Like climbing stems in many respects are creeping or 

 trailing stems, such as those of Partridge Berry and Ground 



Fig. 129. — The rhizome, or root.stock, with ascending shoots, of a 

 Sedge ; X i- , (From Le Maout and Decaisne.) 



Pine. Since the ground supports them, they remain slen- 

 der, and simple in structure. This habit merges over imper- 

 ceptibly into that where the stems run, not on the surface 

 but just beneath it, as in some Ferns and the Grasses; and 

 remarkable self-adjustive adaptations have been described 

 whereby the stems are kept at a constant depth. This habit 

 is best developed in the Grasses and Sedges, where the slender 

 underground stems branch and interlock so profusely as to 

 form the familiar turf, from which rise short vertical stems 

 bearing the foUage (Fig. 129). When thus underground, the 

 stems lose their green color and acquire the aspect of roots, 



