30 Wisconsin Academy of Sciences, Arts, and Letters. 



duced on the side of a stem opposite a wound is assumed to have 

 phylogenetie 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 phylogenetie 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 oaks 

 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 rays and the surrounding tissues. If the claim 

 made by Klebs" 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 



BB Groom, P. The evolution of the annual ring and medullary ray In 

 Quercus. Ann. Bot. 25:983-1003. 1911. 



M Jost, L. Ueher einige Eigenthiimlichkeiten des Cambiums der 

 Baume. Bot. Zeit. 59:1-24. 190L 



" Nordlinger, H. Wirkung des Rindendruckes auf die Form der 

 Holzringe. Centbl. Gesam. Forstwesen. 6:407-13. 1880. 



«' 1. c. 



