NOTES AND ABSTEACTS. 



255 



The author has also some interesting remarks on heather, or heath, 

 which sm^vives in places where it would not pay either to cultivate or 

 afforest. When left alone and protected from grazing, these heaths 

 would be overgrown by forest or wood, and partly at least develop 

 eventually into moor (i.e. peatmoss). Such a moor, when it had 

 increased in height to a certain level, would be annexed by heather over- 

 growing the dead sphagnum, a'nd again be covered by wood. 



The sub-alpine plants characteristic of the Vosges agree best with 

 those of the Pyrenees; there are fewer of them on the Alps, and still 

 fewer in the Black Forest. The Hartfelds are without question former 

 woodlands on which ruderal plants have established themselves. 



G. F. S.-E. 



Mechanical Tissue in Stems, Effect of Tension on the Forma- 

 tion of {Bot. Gaz. vol. xlviii. pp. 251-274; October 1909).— Mr. 

 John S. Bordner gives a short resume of previous experiments dealing 

 with the effect of a pull or traction in developing mechanical tissue in 

 stems. 



His experiments are fully explained, and figures are given showing 

 the differences found between the experimental and the control plants 

 in every case. 



The results may be perhaps most clearly shown by the following 

 table : — ■ 



Average Increases per cent, in 





Breaking 

 Strength 



Xylem 

 Area 



Cross Sec- 

 tion Hard 

 Bast Wall 



Number of 

 Hard Bast 

 Elements 



Thickness 

 Xylem Wall 



Helianthus annuus, greenhouse . 



57-6 



40 



16 



12-5 





Helianthus annuus, field . 



19-6 











Helianthus annuus, field . 



5-8 











Sinapis alba, field 



32 



-10 



52 



38 



5 



Phaseolus vulgaris, greenhouse . 



33 



22 



15 







Phaseolus vulgaris, greenhouse . 



42-5 







14-9 





Vinca major .... 



15-2 











Vinca major .... 



18 



30 



13 





13 



Eicinus communis 



6-4 



4 







•1 micron 



Kubus occidentalis 





-30 



13-6 







Vieia Faba 



21 



8-3 





14-8 





Lupinus albus .... 





14 





m 





The author concludes that actively growing herbaceous stems do 

 respond to traction along their longitudinal axes by increasing their 

 breaking strength and by the development of mechanical tissue. Inter- 

 nodes which had finished their growth were in two instances unable to 

 respond.— G. F. S.-E. 



Medicinal Barks, American. By Ahce Henkel {U.S.A. Dep. 

 Agr., Bur. PI. Ind., Bull. 139, June 1909; plates). — This paper gives 

 a catalogue of the twelve official native American barks — that is, the 

 twelve out of the seventeen recognized in the latest revision of the United 

 States Pharmacopoeia, which are furnished by indigenous or introduced 

 trees and shrubs. It also includes the twenty- three other non-official 



