The Profound Effect on the Structure of Plants 75 



leaf-like stem than by re-developing the lost leaves. It is probable 

 that some pecuharity of this kind in the past history of the plant 

 will explain in each case such curious features, the course of devel- 

 opment being always that which offers the least resistance at the 

 moment. 



The reader will now be prepared, I think, to admit that of all 

 the influences concerned in the determination of plant form, — 

 indeed in making plants what they are, — the most important by 

 far is the physiological process of food-making, or photosynthesis, 

 and that the feature of this process having the most profound 

 effect is the need for exposure to hght. 



