Medullary Rays of Querctts , 989 
eclipse of the bounding line of tracheides is more complete. Thus 
Q. incana is the species with the most indistinct rings. 
But the most remarkable ring is that of Q . ( Pasania ) fenestrata , 
Roxb. (Fig. 12), in which the vessels show no detectable distinctions in 
size that are associated with their position in the ring. The outer boun¬ 
dary of the ring in most places is clearly defined by a line of flattened 
fibro-tracheides, though the line becomes obscure here and there. This 
ring, however, presents the appearance of being broken up into separate 
segments; for here and there are to be seen pairs of larger medullary 
rays which are separated by a mass of tissue that is devoid of vessels, 
and in this separating tissue the tangential line of flattened tracheides 
marking the boundary of the ring is so much nearer the centre of the 
stem that it presents the appearance of being continuous with the middle 
zone of the ring on the other sides of the rays. This peculiar apparent 
disruption of the ring will be explained later in the present paper. 
Comparison of the different types. 
The annual rings of typical deciduous species are marked by three 
features:— 
1. Presence of large vessels contrasting greatly with the smallest vessels. 
2. The concentration of the largest vessels in the spring zone. 
3. The approximation of the vessels in the spring-zone to form con¬ 
centric series. 
In evergreen species there is a tendency for decreased size of the 
vessels, decreased difference in the sizes of the vessels in the ring, centrifugal 
transference of the maximum size of vessel to the middle of the ring or 
irregular distribution of the wider vessels in the ring, and finally increased 
tangential separation of the vessels in the spring-zone. 
In order to give a statistical basis to my observations I made a number 
of measurements of the diameters of the vessels and of the tangential 
distances apart of the vessels in the inner (spring) zone. Having already 
arranged the species in order according to distinctness of the pore-zone as 
judged by inspection, I tested this order by means of the measurements 
made, and was able to form some idea as to the extent to which the 
various changes in the arrangements, sizes, and number of vessels move 
along parallel lines in evolution. 
The measurements are given in the succeeding table, all being given in 
millimetres representing magnifications of twenty-five diameters. The 
diameters of the vessels were obtained by taking the mean of two diameters 
at right angles. 
Commencing at the left-hand side, the first column gives the name of 
the species and its habit. Evergreen (E.), sub-evergreen (SE.); the letters 
3 T 
