SAPSUCKERS AND THEIR GUESTS. 153 



the tongues of other woodpeckers. In form it 

 is not adapted to use as a dart for securing 

 insects, and its fringed edges have suggested to 

 biologists who were not observers of the bird's 

 habits that sap might, as in the cases of species 

 with similar apparatus, form an important por- 

 tion of its food. The following extract from 

 a letter written to me by Mr. W. F. Ganong, 

 Instructor in Botany at Harvard University, 

 gives a clear history of the progress of sap in its 

 ascent and descent. 



"It is now thought by botanists that the elab- 

 orated sap from the leaves is transferred down 

 the stem through the soft bast cells of the inner 

 bark, just outside of the cambium layer. It 

 hence passes to the medullary rays, where it is 

 stored up to last over the winter in the form of 

 starch chiefly. Some of it is stored also in the 

 wood cells of the young wood — but none I 

 believe in the ducts or fibres or main masses of 

 the wood itself. In the latter there is a current 

 of crude sap from the roots flowing up, but I 

 do not think any botanist thinks that the elabo- 

 rated sap flows down by the same path. Hence 

 if the woodpecker in July or August penetrates 

 the loood^ he would get only crude sap from the 

 ordinary wood tissue, but he might get elaborated 

 sap from the medullary rays or some of the 

 smaller wood cells — much more of the former 



