210 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



of other trees, taken from tables similar to that just 

 quoted. 



Thus it may be seen that the area occupied by the lumina 

 of the living cells varies from about one-tenth (Salix) of, 

 to almost equality (Acer) with, the area of the lumina of 

 the tracheae, the mean being about one-quarter. The 

 latter may fairly be taken as a representative value, for 

 it is based on twenty-two observations on seven kinds of 

 trees. 



TABLE LV. 



MEAN VALUES FOR AREAS OF THE CELLS, TRACHEAE, AND WALLS, IN A 

 CROSS-SECTION OF THE WOOD OF A DICOTYLEDONOUS STEM. 



Quantitative experiments of this type serve to clarifv 

 one's ideas on the anatomy of woody stems, and further 

 data of this nature would no doubt prove very useful. The 

 labour, however, necessary to obtain them is very con- 

 siderable. 



The foregoing study of the distribution of the storage 

 cells and tracheae of the wood clearly shows how the view 

 as to the nutritive character of the transpiration stream is 

 in accord with the histology of the stem. The role assigned 



