IN CEYLOX. 25 



length of the members of the vessels from O30 to 0-54 mm. 

 This constancy in size throughout the genus in Ceylon is one 

 of the main characters of the timbers. When one considers 

 the climatic differences between Mannar and Adam's Peak 

 Wilderness, one is led to expect that there will be great 

 differences in the size of the water storing and conducting 

 tissues in the species growing at these places, but such 

 differences are by no means pronounced. 



There is very little variation in the form of the members 

 of vessels. In the heartwood the small-lumined vessels are, 

 when isolated, approximately spherical or crudely hexagonal 

 in transverse outline, but as one passes to the sapwood the 

 increase in dimensions is more in the radial than the tangen- 

 tial direction, and as a consequence a radially elongated 

 element presents itself. When the members are grouped, 

 however, the spherical or elongated outline is rarely met 

 with, one or more sides become straight, and the tangential 

 diameter of each member is usually considerably more than 

 the radial. 



The sides of each member are characterized by a straight 

 vertical course, and the original transverse partitions are 

 only slightly inclined to the horizontal. 



The walls of the vessels vary in thickness from 0'002 to 

 0-0035 mm. They are usually very well pitted. They are 

 composed mainly of lignin, which continues to respond to 

 the safranin and fuchsin tests even when considerably dis- 

 coloured, and the lumina partially filled with coloured 

 materials. 



The function is probably that of storing or even conduct- 

 ing water, but when once the lumina are filled with gum and 

 resin this function must be taken up by the younger 

 tracheal elements. The vessels do not undergo depletion of 

 coloured contents, the infiltrating materials increasing from 

 time to time until the vessels are completely blocked. 



Tracheids. There is not very much to be said about these 

 elements. They are only very sparsely distributed, and in 



8(1)4 (4) 



