42 

 petioles or iiBanclies. While in Dicotyledons there is great ability 

 for branching and leaf display, the stem gives nothing to the plant 

 but mechanical support. In some plants it may be better not to 

 have so great a chance for leaf display since it requires so strong 

 a mechanical support. This necessitates a large supply of food. 



The stems of fungi may be connected with reproduction, and 

 sporophytes in mosses, with the same thing. In most of the rosette 

 type, the chietf use of the stem is probably for purposes of 

 reproduction and it may also have influenced the long stem of the 

 mullein. The same principle is true though perhaps in a less degree 

 in trees, since many trees are aneraophilous. 



The cylindrical stem is most common, then the square, and lastly 

 the triangular. Sometimes we find the flat stem. The cylindrical 

 is probably the strongest. Roiind and square stems can best bear the 

 weight of their branches. Shape of stem may be influenced by wind 

 which if prevailing may elongate the diameter of the stem in 

 direction of the wind changing a cylindrical stem to an elliptical 

 one. Tree stems need mechanical support and trees usually have 

 rounded stems. Where there is little need for protection a square 

 stem may answer better than a round one since it requires less 

 strengthening tissue. Square and triangular stems have more surface 

 in proportion to volume, hence can do more chlorophyll work. 



Coccoloba, an extreme xerophyte, is the best example of a 

 flattened stem. It has lost its leaves and the flat stem does the 

 leaf work. Round stems have less surface, hence less transpiration. 

 Color of Bt ems . 



