30 Wisconsin Academy of Sciences , Arts, and Letters. 
duced on the side of a stem opposite a wound is assumed to have 
phylogenetic significance. 
According to Groom 55 the evolution of the rays in Quercus is 
not as simple as presented by Eames, Bailey, Thompson and 
others for he found cases where the primary rays seemed to 
branch like those of beech described by Jost 56 as well as others 
where the aggregations occurred in the manner described in the 
above cited papers. Groom is inclined to the view that ray de¬ 
velopment and architecture is based on physiological rather than 
on phylogenetic factors and that it is impossible at present to 
decide whether the narrow or the broad-rayed type is the more 
primitive. 
It is also worth noting that, although Nordlinger 57 found the 
valleys originating along the groups of broad rays and that oak3 
without the broad rays are devoid of valleys, in case of very 
large old trees the ridges were often found to occur along the 
broad rays, while valleys were present between them, i. e. just 
the reverse of the conditions obtaining in younger specimens. 
Perhaps it might prove worth while to find out whether the 
occurrence of valleys and ridges in such trees is due to differ¬ 
ences between the rate of growth in the wood and in the rays 
rather than being due to an early cessation of ray growth as 
Sorauer had assumed. In case the formation and radial elonga¬ 
tion of ray cells were very slow as compared to the radial in¬ 
crease in the wood cylinder in general, it is conceivable that the 
solid broad rays may have a dominating influence and retard 
radial growth on both sides of them because of the firm attach¬ 
ment between the raj^s and the surrounding tissues. If the claim 
made by Klebs 57 that the presence of large quantities of elab¬ 
orated food retards radial growth should prove correct and since 
these large rays are the storage reservoirs for elaborated foods 
it would also be understandable how they might be comparative¬ 
ly slow growing in youth and comparatively more rapid in old 
age, when radial growth has become slow. 
The conspicuous ridges on the lower part of trunks correspond 
56 Groom, P. The evolution of the annual ring and medullary ray in 
Quercus. Ann. Bot. 25:983-1003. 1911. 
66 Jost, L. Ueher einige Eigenthiimlichkeiten des Cambiums der 
Baume. Bot. Zeit. 59:1-24. 1901. 
47 Nordlinger, H. Wirkung des Rindendruckes auf die Form der 
Holzringe. Centbl. Gesam. Forstwesen. 6:407-13. 1880. 
67 1. c. 
