354 RELATION TO ENVIRONMENT. 



tion of the problem in the relation of the shoot to aerial en- 

 vironment, stem and leaf have in most cases cooperated;* but 

 in view of the great variety of stems and their modifications, as 

 well as of leaves, it will be convenient to discuss them in separate 

 chapters. 



693. (2d) Shoots without foliage leaves. These are subter- 

 ranean or aerial. Nearly all subterranean shoots have also 

 aerial shoots, the latter being for the display of foliage leaves 

 (foliage shoots), and also for the display of flowers (flower shoots). 

 The subterranean kinds bear scale leaves, i.e., the leaves not 

 having a light relation are reduced in size, being small, and they 

 lack chlorophyll. Examples are found in Solomon's seal, man- 



Fig. 4130. 



Burrowing type, the mandrake, a "rhizome." 



drake (fig. 41 3 a), etc. Here the scale leaves are on the bud at 

 the end of the underground stem from which the foliage shoot 

 arises. Aerial shoots which lack foliage leaves are the dodder, 

 Indian pipe-plant, beech drops, etc. These plants are sapro- 

 phytes or parasites (see Chapter IX). Deriving their carbo- 

 hydrate food from other living plants, or from humus, they do 

 not need green leaves. The leaves have, therefore, probably 

 been reduced in size to mere scales, and accompanying this 

 there has been a loss of the chlorophyll. Other interesting ex- 

 amples of aerial shoots without foliage leaves are the cacti where 



* It is interesting to note that in some foliage shoots the stem is entirely 

 subterranean. See discussion of the bracken fern and sensitive fern in 

 Chapter XXXIX. 



