156 MORPHOLOGY AND LIFE HISTORY 



Of what significance, in this connection, is their 

 profuse branching? 



(e) Describe the surface of the stem along the 

 internodes, noting the presence or absence of 

 ridges, the hardness (or otherwise), and the 

 "feel" of the surface. To what are the last 

 two characters due? 



(/") If material of Equisetum hyemale (the " scour- 

 ing rush") is available, it will be instructive to 

 burn a portion of the stem in a Bunsen flame, 

 and to examine the unburned portion under 

 a microscope. The preservation of the cell- 

 walls, uninjured by the flame, is due to the 

 fact that they are impregnated with silica, 

 taken up by the plant from the soil in the 

 form of a silicate, and secreted by the proto- 

 plasm of each individual cell. It is the pres- 

 ence of the silica that made this species useful 

 for scouring cooking utensils, and thus gave it 

 its common name. 



2. The Leaves. 



(a) Describe the shape and character of the leaves; 

 their arrangement on the stem (i.e., opposite, 

 alternate, or whorled). 



(b) Do the leaves function in the work of photo- 

 synthesis? In what orgarl or organs is that 

 function performed? 



(c) To what, in the fern, are the branches of the 

 vegetative part of the stem analogous? To 

 what are they homologous? To what, in the 

 fern, are the scales at the nodes analogous? 

 To what are they homologous? Explain. 



3. The Roots. 



(a) Briefly describe their character and distribu- 



