1002 Groom .— The Evolution of the Annual Ring and 
Any one or a number of these features may be wholly or totally 
lacking. 
There is a certain degree of correspondence between the habit and the 
arrangement of the large vessels in the annual ring of Quercus . Species 
showing the most striking pore-zone are deciduous ; those showing it 
regularly and distinctly but not having so marked a disproportion in size 
between the innermost and outermost vessels are sub-evergreen ; whilst 
those species with no trace of a pore-zone are truly evergreen ; finally, the 
transitional forms, including both evergreen and sub-evergreen species, have 
feebler or more irregular indications of the porous spring-zone, which in its 
simplest condition assumes the form of a simple concentric series of widely 
separated vessels. In a previous paper (TO) I have shown that in 
American species the maximum calibre of vessel varies with the habit, 
being greatest in deciduous, least in truly evergreen, and intermediate in 
sub-evergreen species. 
In none of the species examined by me are all traces of annual (or 
growth) rings lacking, though in some evergreen species the boundaries of 
these are in places difficult to follow, and in Q. fenestrata the annual ring 
presents the appearance of being broken up into distinct arcs differing in 
the length of their radii. 
All species of Quercus possess uniseriate shallow medullary rays, while 
some species also have broad high multiseriate rays. 
Between multiseriate and uniseriate rays there exist in various species 
numerous transitional stages representing either disintegration of the broad 
ray into a number of narrow ones or integration of numbers of narrow rays 
to build up the broad ray. 
It is impossible at present to decide whether in Quercus the broad- 
rayed or the narrow-rayed type was primitive. Pointing in favour of the 
latter view are the observations of Bailey and Eames that in seedlings of 
Quercus and Alnus the narrow rays gradually link up to form broad ones. 
But pointing in the opposite direction are Jost’s statements that in the 
inner rings of Fagus the broad high rays when traced outwards undergo 
division into smaller ones, while Tabor’s observations on the seedling 
of Fagus show that both kinds of change are going on simultaneously in 
the rays of the same annual ring. In Quercus fenestrata the structure and 
paired arrangement of certain high rays strongly suggest that disintegration 
of the broad rays in a phylogenetic sense has taken place. 
In American evergreen species of Quercus , excluding Pasania , there 
is a striking parallelism between, on the one hand, the distinctness of the 
annual ring as judged by the size of the vessels in the spring-zone, and, on 
the other, the thickness and degree of subdivision of the broad rays (or the 
thickness and degree of aggregation of the narrow rays). The parallelism 
is disturbed in American species by differences due to genetically distant 
