CHAP. I.] 



PLANT ARCHITECTURE. 



43 



thing known as a terminal leaf, and a thin vertical slice 

 of a young bud examined under the microscope will show 

 the youngest leaves to be truly lateral in origin, the 

 centre or actual apex of the stem being composed of 

 undifferentiated fundamental tissue. 



From these young leaves the rudimentary fibro-vascular 



Fig. 13. Diagrammatic re- 

 presentation of a section of a 

 palm stem, showing the ar- 

 rangement and direction 

 taken by the fibro-vascular 

 bundles that originate in the 

 leaves and pass down the 

 stem. 



bundles pass downwards into the stem, where they usually 

 join on to older bundles and become arranged in various 

 ways depending on the group to which the specimen 

 under examination belongs. Fibro-vascular bundles that 

 originate as above from leaves are usually called foliar 

 vascular bundles, or leaf-traces. From the above state- 

 ment it will be seen that the increase in size of the trunk 

 and branches, in other words, the formation of the fibro- 

 vascular element, which constitutes that portion of the 

 trunk popularly known as " wood," is entirely dependent 

 on the presence of leaves ; consequently, if during any 

 given season the leaves of a tree are destroyed by insects 

 or prevented by any means from attaining their full 



