75 
Origin of Wood Parenchyma. 
To those who are familiar with the modern theory of the origin of 
wood parenchyma it is at once clear that we have here direct testimony 
from a fossil form as to the correctness of that view. It has been shown 
that in Spruce wood, for example, elements are laid down at the end of the 
SUMMER SPRING 
Text-fig. 2. 
Text-fig. 3. Picea. Origin 
of parenchyma. 
growing season which at an early stage ‘ become transversely septate, and in 
the segments so set off the protoplasm sometimes persists (when a typical 
parenchymatous dement of the wood is the result) ; at other times it 
disappears with the complete differentiation of the walls surrounding it (in 
the case of so-called short tracheides) \ Text-fig. 3 illustrates this condition 
in a diagrammatic manner, while Fig. 6, PI. Ill, is introduced to show by an 
