Grossenbacher—Radial Growth in Trees. 
29 
tranks of Carpinus, etc., and that the wood of these valleys con¬ 
tains the large aggregate rays while that in the ridges has simple 
ones. That the presence of the aggregate rays has induced the 
valleys by their early cessation of growth as Sorauer 50 held does 
not necessarily follow, though it may be true, as it is more re¬ 
cently implied by Bailey 51 and others. In. a number of recent 
papers written by Jeffrey’s students 52 it is maintained that the 
different types of rays and their method of development are of 
great phylogenetic significance in showing the paths of evolu¬ 
tionary development. Yet in the above cited paper by Bailey 
it is also noted that changed nutrition may markedly modify the 
rays and their distribution. 
Some of Kny’s 53 results obtained in his experiments seem to 
indicate that the pressure under which rays differentiate in the 
cambial zone has much to do in determining their sizei He 
found on applying a pinch-cock to twigs of Salix and Aesculus 
Hippo cast anum in spring that not only was radial growth almost 
entirely inhibited on the compressed sides but that the ray cells 
were broader in tangential direction and that in some cases a 
doubling of the typically simple rays had occurred in both trees. 
In the above cited paper on the causes of excentric growth Mer 
also calls attention to the increase of radial growth on trunks 
opposite a wound. This observation of Mer’s is of interest here 
chiefly because the occurrence of traumatic rays 54 in wood pro- 
eo Sorauer, P. Handbuch der Pflanzenkrankheiten. Zweite Auflage. 
1:537. 1886. 
61 Bailey, I. W. The relation of the leaf-trace to the formation of 
compound rays in the lower Dicotyledons. Ann. Bot. 25:225-41. 1911. 
52 Bailey, I. W. Reversionary character of traumatic oak woods. 
Bot. Gaz. 50:374-80. 1910. 
Eames, A. J. On the origin of the herbaceous type in the Angio- 
sperms. Ann. Bot. 25:215-24. 1911. 
Thompson, W. P. On the origin of the multiseriate ray of the Dico¬ 
tyledons. Ann. Bot. 25:1005-14. 1911. 
Holden, R. Reduction and reversion in the North American Sali- 
cales. Ann. Bot. 26:165-73. 1912. 
Bailey, I. W. The evolutionary history of the .foliar ray in the wood 
of the Dicotyledons, and its phylogenetic significance. Ann. Bot. 
26:647-61. 1912. 
53 Kny, L. Ueber den Einfluss von Zug und Druck auf die Reichtung 
der Scheidewande in sichtheilenden Pflanzenzellen. Jahrb. Wiss. Bot. 
37:55-98. 1902. 
64 Jeffrey, E. C. Traumatic ray-tracheids in Cunninghamia sinensis. 
Ann. Bot. 22:593-602. 1908. 
Bailey, I. W. Reversionary characters of traumatic oak woods. Bot. 
Gaz. 50:374-80. 1910. 
