DIV. I 



MORPHOLOGY 



117 



forms on the flowering shoots are essentially different in form from 

 those which the plant has previously borne. This difference is even 

 more marked in Eucalyptus globulus, which first bears oval sessile leaves 

 and then sickle-shaped leaves. Not uncommonly the lowest leaves 

 of the seedling (juvenile or primary leaves) are more simply formed 

 than the later leaves. The . 



opposite case is illustrated r^ 1 _J x "Vv. 



by Acacia (Fig. 136). 3| <* "^ \ 



B. The Seed-leaves or ^^ 



Cotyledons may be stalked 



\ / \ 



I 



FIG. 134. Selaginella Martensii. Ani- 

 sophylly of the dorsiventral shoot. 

 On the upper side of the stem are 

 two rows of smaller asymmetrical 

 green leaves and on either flank a 

 row of larger asymmetrical leaves 

 (slightly magnified). 



FIG. 135. Ranunculus aquatilis. ub, Submerged leaves ; 

 sb, floating leaves ; b, flower ; /, fruit. (Reduced. 

 After SCHEXCK.) 



or sessile, and are always more simple in form than the foliage leaves. 

 They often, however, exhibit the same plan of segmentation. 



The cotyledons may remain below the soil enclosed in the seed -coat 

 (HYPOGEAL). In this case they are usually fleshy structures serving to store 

 reserve food material and are composed largely of storage parenchyma. EPIGEAL 

 cotyledons, which burst the seed-coat and appear above ground, tend to become 

 green and then for a period assimilate carbon dioxide like the foliage leaves. In 

 Monocotyledons, which have a single cotyledon, only the sheath of this as a rule 

 emerges from the seed. It may remain below ground and colourless, or grow up 

 and turn green. 



C. The Scale Leaves and Braeteal Leaves, while indistinguishable 

 from the foliage leaves in the early stages of development, are less 



