Grossenbacher Radial Growtli in Trees. 29 



trunks 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 size. He 

 found on applying a pinch-cock to twigs of Salix and Aesculus 

 Hippocastanum 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- 



60 Sorauer, P. Handbuch der Pflanzenkrankheiten. Zweite Auflage. 

 1:537. 1886. 



61 Bailey, I. TV. The relation of the leaf-trace to the formation of 

 compound rays in the lower Dicotyledons. Ann. Bot. 25:225-41. 1911. 



5 ~ 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. TV. The evolutionary history of the foliar ray in the wood 

 of the Dicotyledons, and its phylogenetic significance. Ann. Bot. 

 26:647-61. 1912. 



63 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 Jeffrev, 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. 



