10 



PROPERTIES OF Wool). 



opposed to those that represent vessels as the chief conductors 

 of water ; they show that vessels normally never contain water, 

 but serve exclusively for aeration and for conducting oxygen 

 to the neighbouring parenchymatous cells, which are rich in 



Fig. 2. Sprucewood. 



1, Natural size. 2, Small part of one ring magnified 100 times (the 

 vertical tubes are wood-fibres, in this case all " tracheids "). m Medullary, 

 or pith, rays, n Transverse tracheids of pith-rays, with simple pits. 

 except in lowest row. a, I, and c Bordered pits of the tracheids, 

 enlarged. Hartig. 



plasma. For this and several other reasons, the theories of 

 R. Hartig * ascribing the formation of abundant spring- wood to 

 the great demands of a tree for water are considered erroneous, 

 and so is his treatise regarding the influence of nutriment and 

 transpiration on the strength of wood, as if that depended on 

 the volume of all the vessels in a tree. 



* R. Hartig, " Holzuntersuchungen." lierlin, linn. 



