GLIMPSES INTO PLANT STRUCTURE 55 



of a leaf stalk — there are many plants which pro- 

 duce only a single leaf— and the leafstalk in turn 

 bears the same relation to the mid-rib of the leaf 

 So, in Fig-, t^j^ I show the internal structure of 



I'^o- 37- ^'he structure of the mid-rilj, or central vein of a 

 rhododendron leaf 



the mid-rib of the leaf of a rhododendron. There 

 are some leaves, moreover, which apparently have 

 no mid-rib, or are all mid-rib. It would be diffi- 

 cult, for instance, to say how much of the needle 

 of a pine-tree was " blade " and how much " mid- 

 rib " and "nerves" when viewed externally, but 

 the microscope reveals, when the leaf is seen in 

 section, that the vascular strands of the mid-rib 



