ISO 



Hanging gourd fruits, Vifhich develop more abundant mechani- 

 cal tissue in their stalks than dp the varieties v/hich lie upon 

 the grotfnd, and the like have made it seem probahle that an in- 

 crease of mechanical tissue can be called forth by increased me- 

 chanical demand upon it, Wiedersheira's experiments have fur- 

 nished exact proof of this, Future research will have to deter- 

 mine whether the tissues of different plant organs are equally 

 suited for the formation of activity-hyperplasias, v^^hether fur- 

 ther only a few varieties are capable of it and whether finally 

 by means of special conditions the organs, of which much is re- 

 quired, can possibly be made capable of an abundant development 

 of their mechanical tissues, 



^j A contribution on the last named case may be given here. 

 Kochting'^ reported recently on experiments with stalks of 

 Brassica oleracea var, sabada (savo3r) which were placed horizon- 

 tally and strained at the tip by means of hanging weights. On 

 the upperside of the branch, under, the influence of the mechan- 

 ical requirement, an activity-hyperplasia was produced by abnor- 

 mally lively growth in thickness. In the present case oiily one 

 side of the object under experimentation was taxed by the 

 strain, - it would be conceivable that the very inequality of 

 the conditions under which the different parts of an aacis develop 

 favoi-s the production of an activity-hypeirplasia. 



Vochting's reseai-ohes have shown savoy to be a plant in 

 which hyperplastic tissue changes occur on the side strained by 

 bending. Future research Will certainly make known other ob- 

 jects, in which the side taxed by the pr essur 6 reacts in the same 

 way to the mechanical demand made upon it . In my opinion the 

 foriKi.tion of the red wood fbois rouge) of spruce and hemlock 

 trunks favors this. This modnLfication of the strengthening tis- 

 sue, characterized by a red-brown coloration shafts broader annual 

 rings, richer in cells, than does the normal wood. It consists 

 (143) chiefly or exclusively of thick walled tracheids, which are some- 

 what shorter than the noriml ones, often leaving perceptible in- 

 tercellular spaces between them and conspicuous because of the 

 spiral structure of their thickening layers, Hartig saw redwood 

 regularly produced on the underside of horizontal branches and 

 further in tree trunks on the side Opposite the one exposed to 

 the wind, when they were especially exposed to its action be- 

 cause of their position in the open, in short, in those places 

 which were especially strongly taxed by mechanical pressure . In 

 regions in which westerly winds prevail, the redwood side is al- 

 ways the one facing the Easf^, 



^ Zur experiraentellen Anatomie, Machr. K. Ges, Wiss., 

 Oottingen, 1902, Heft 5. 



■ ^ As the most important literature on redwood, compare 

 Hartig, R,, Das Eotholz der Piohte. porstl.-Waturw. 2eitachr., 

 1896, Bd. V, p, 96; further Holzuntersuchungen, Altes und Heues, 

 1901, Compare also Mer, De la formation du bois rouge dans 1© 

 sapin et IfBpicAa. 0, R. Acad. So. P^ris, 1887, T. CIV. p, 376. 

 Cieslar, Das Rotholz der Pichte. Obi. gee Forstwesen, 1896, p. 

 149. Anderson, Ueb, abnorme Bildung v. Harzbehaltern uijd andere 

 zugleich auftretende anat. Verand, im Holz erkrankter Coniferen, 

 Forstl.-Haturwiss, Zeitechr.. 1896, Bd. V, p, 439. Observations 

 on the influence of the wind on the unequal increase in thick- 

 ness of trees extend back as far as Knight (1803), according to 

 whose statements, the annual rings on the sides taxed mechani- 

 callv (by bending) are broader tteip on the others. Compare fur- 

 ther" Busgen : Bau u. Leben d, WalJt^baume , Jena. 1897, p. 67, and 

 the literature there oited. ;' 



