432 Scientific Proceedings. Royal Dublin Society. 



uud vei-anlasste sie so zur Erzeugung mechauischer Zellen." So Voohting 

 at aii3^ rate considers the mecliaiiical factor of importance in a case very 

 similar to ours — abnormal secondary tissue in a tuber bearing a large 

 vegetative development above and roots below. Indirectly he might be 

 adduced against Ball and Wiedersheim and Hibbard as contending that 

 their methods of applying a mechanical stimulus were inaccurate, and that 

 positive results should result from a properly acting stimulus. Such results 

 were recently obtained by Bordner (35) in 1910. He subjected plants — the 

 same species it may be remarked as were used by Ball and Hibbard — to 

 longitudinal tension for prolouged periods. The work was carefully and 

 accurately carried out with many individuals under tension and many 

 controls. He concludes tlius — " The results of the experiments have con- 

 vinced the writer conclusively that actively growing stems of the herbaceous 

 plants used, and of Vinca major, respond to traction along their longitudinal 

 axis by increasing their breaking strength, and also by increased develop- 

 ment of bast, or of xylem, and in most cases by an iacrease of both these 

 mechanical tissues." Thus an average of about thirty plants of Helianthus 

 (innuus loaded on November 21st with 25 grammes, gradually increasing to 

 300 grammes on December 4th, the experiment ceasing a few days after- 

 wards, gave the following results :— 



Breaking strength increased .... 57'6 per cent. 

 Cross-section of walls of hard bast increased . 16 per cent. 

 No. of hard bast elements increased . . . 12'8 per cent. 



Total xylem area increased . . . .40 per cent. 



This is a remarkable positive result which cannot be gainsaid. And 

 when we remember that one of the functions of the xylem is undoubtedly 

 support, we cannot afford to ignore the mechanical factor if it may cause as 

 great an increase in the xylem as 40 per cent. 



Again, it has long been known that tendrils after attachment to the 

 support show an increase in mechanical tissue and in resistance to breaking 

 strains (see Worgitsky 36). How far this is a response to the stimulus of 

 contact, and how far to that of tension, has been long disputed. Thus Fitting 

 (37) claims that the stimulus of contact is active to the very base of the 

 tendril, while Newcombe (38) and MeDougal (39) affirm that its effect is 

 much more localized, hardly extending at all beyond the tip. Quite recently, 

 however. Brush (40) had made an endeavour to analyze the effects of tension 

 and oontact in the tendrils of Passiflora caerulea, coming to the conclusion 

 tliat considerable increase in the breaking strength is produced by contact 



