Grossenbacher Radial Growth in Trees. 41 



the last ring but in a more recent study Jahn 77 made it appear 

 that the entire alburnum may be more or less active in water 

 conduction although perhaps as much as half or more of the 

 water is thought to be carried up the last ring. 



Some evidence of the fact that wind is both a formative and 

 a limiting factor in plant growth is afforded by several scat- 

 tered papers on the influence of wind on vegetation, a few of 

 which might be briefly noted in this connection. 



While making an experimental study of the effects of wind 

 on vegetation Bernbeck 78 obtained some interesting results. 

 He found that both shoots and leaves of plants subjected to 

 wind of 14 m. or less per second were injured in proportion to 

 the amount of swaying and bending induced and that even del- 

 icate leaves of shade plants are not injured by the wind if they 

 are firmly held to prevent swaying or bending during the ex- 

 posure. It was found that the production of organic food was 

 reduced in leaves exposed to wind as compared to that accum- 

 ulating in protected leaves. 



Gilchrist 79 reported that potted plants of Helianthus annuus 

 subjected to artificial wind swaying and rocking did not grow 

 as tall as the checks while the diameter of their stems exceeded 

 that of the check plants. Some more recent observations by 

 Cavara 80 show a similar effect of wind exposure on the struc- 

 ture of Iresine, Coleus, Aster, Zinnia, and Sempervivum. 



Esbjerg 81 found that protecting various herbaceous plants 

 from strong winds by means of screens resulted in an increased 

 yield. An increase of 16 to 31% above that of the checks was 

 secured in the yield of grain from rye ; the yield of ruta-baga 

 roots was increased from 7 to 17% and of mangels from 3 to 

 18%, while clovers and grasses showed a gain of from 4 to 23% 

 as a result of wind protection. 



77 Jahn, E. Holz und Mark an den Grenzen der Jahrestriebe. Bot. 

 Centbl. 59:257-67; 321-29; 356-62. 1894. 



78 Bernbeck, 0. Der Wind als pflanzen-pathologischer Faktor. In- 

 augural Dissert. Bonn. 1907. pp. 116. 



78 Gilchrist, M. Effect of swaying by the wind on the formation of 

 mechanical tissue. Report Mich. Acad. Sc. 10:45. 1908. 



80 Cavara, F. Some investigations on the action of wind on plant 

 growth. Expt. Sta. Record. 25:224-25. 1912. 



81 Esbjerg, N. Experiments with windbreaks. Expt. Sta. Record 

 23:435. 1910. 



