136 Introduction to Botany. 



112. Determine, as above, the morphology of the ten- 

 drils of the wild smilax and Virginia creeper, or grape. 



113. Work out the evidence for the morphology of the 

 spines of barberry. 



114. Determine the morphology of all structures which 

 are borne on the stems of Asparagus medioloides (green- 

 house smilax). 



115. What is the morphology of the prickles of rose 

 and gooseberry ? 



116. Determine the morphology of an onion bulb. 



117. What is the morphology of the tuber of Irish 

 potato, and of the structures borne on it ? 



1 1 8. Determine the morphology of the bladders of 

 Utricularia or bladderwort. 



DISCUSSION. 



108. Diversity of Plant Forms. The great diversity of 

 plant forms, as we now find them, has doubtless been 

 evolved from comparatively few and simple forms. No 

 two plants are entirely alike, and probably no structure is 

 exactly like any other of the same kind. Compare the 

 leaves on a plant and note how dissimilar they are in form, 

 size, and outline, and what endless varieties of leaves are 

 on the different kinds of plants. Such facts as these are 

 an expression of the extreme plasticity of the plant body, 

 which seems to respond to external conditions and forces, 

 and to internal tendencies, like clay to the hands of the 

 potter ; yet we must remember that the infinite variety of 

 forms which we now see has been evolving through the 

 untold years since life began upon the earth. 



109. Morphological Elements. After plants had ad- 

 vanced in their evolution from the un differentiated body 

 known as the thallus (see pages 257 to 285) to the forms 



