41 

 Lecture 10, .JUly 23, 1900. 



Stews?. 



One of the most important feat\i.res is the direction. Another, 

 shape ; still another, branching. Color of stems an additional 

 factor. 

 Evolution of stems . 



In the lowest Algae we find no stems. Even higher forms as 

 Ulva have no true stems, but in P\icus we have a true stem, since in 

 the center the cells are closer together giving stiffness. In 

 Algae of the Pacific coast large stems are often found. 



Pungi develop no leaves, but perfect stems as do also liverworts. 

 Mosses show a real stem with definite roots below and definite leaves 

 above. Going up from the mosses, the stemless form is the exception. 



The erect stem is found in a great majority of plants, and was 

 first developed in the mosses. Kerner calls the stem an indirect 

 adaptation to light, but other factors also influence it. In fungi 

 the light relation is insignificant. Another theory is that carrying 

 a plant above the ground favors reproduction, spores or pollen being 

 carried by insects or wind. 



Kerner *s theory with regard to stem is that elongation of 

 internodes fairniBs the development of leaves. In a forest trees are 

 apt to crowd upward towards the light. Palms do not branch but 

 bear all leaves on the erect stem. The greater the branching the 

 greater the chance for leaf display. The petiole further relates 

 the leaf to the light .i. Tree ferns and Monocotyledons have no 



