131 



The branches of conifers are kn&wn to be constructed 

 hsrpo-na^tically. i. g., excentrically, in stich a way, that the 

 horizontal underside of the branches is more strongly developed 

 tl^an is the upperside. I would like conjeoturally to call at- 

 tention to a c onnection between the exoentrlc growth In thiok 

 ness of normal parts of trees and the tendency toward (one^ 

 sided) aot ivity-hyperplasia under abnormal oonditiona* If in 

 conifers .""'"^he horizontal branches of which are developed toore 

 strongly on the underside,- the one taxed by pressure,- than 

 on the upper side, it can be proved that the trunks also are 

 developed hyperplastically on the side especially taxed by the 

 pressure under abnormal conditions, then it may be conjectured 

 that among plants provided with epinastlo branches, whose bran- 

 ches therefore are more strongly developed on the side of the 

 strain we may search for such as will, tinder experimental modt- 

 ification of the mechanical requirement, develop a reinforce- 

 ment of the side strained, (Drees with diplonastloally construc- 

 ted branches will possibly be able to react in the same way to 

 the strain and pressure-, due to a bending of their trunks, by 

 reinforcing their tissues. It would be very desirable if, in 

 connection with our knowledge concerning the formation of red 

 wood, corresponding experiments could be made on daotduous 

 trees and if some one would prove the influence upon growth in 

 thickness caused by a bending continued over several years. 



Besides meclianical tissues, vascular tissues also have an 

 especial interest for us. 



In order to increase the effgctlveness of vascular bunr 

 dies, v/hich under normal oonditions - to conclude from their 

 extent, provide only for the transfer of moderate amounts, I 

 out through the mid ribs of young leaves of numerous dicotyle- 

 dons which are pinnately ribbed (compere fig, 58) in the expeo- 

 (144) tation that possibly the anastomoses well adapted for taking 

 over the v/ater connection between the uppier and lower halves, 

 (fig, 58a), would undergo a more vigorous formation than under 

 normal conditions. The expected did not take place. In most 

 cases the side ribs and their anastomoses are not capable of 

 compensating for the intersected midribs nor of providing suf- 

 ficiently for the upper half of the leqf. This either perishes 

 entirely, or becomes discolored, or the leaf-developiraent pro- 

 gresses abnormally, since leaves with disproportionately wide 

 bases and stunted, tips are formed ( Populua pyramidalis ). How- 

 ever, a more luxuriant development of the side ribs as aotivitya- 

 hyperplasia never took place in the plants which I investigated . 



Further, I made girdling experiments with plants character- 

 ized by medullary phloem bundles (Eucalyptus, Kerium) but I 

 could not prove that in girdled branches the latter had under- 



^ In spite of the, at present, negative results, perhaps 

 a continuation of similar experiments might not be undesirable.- 

 At any rate, nature itself often makes experiments which, agree- 

 ing with what hua just bden described, prove that after removal 

 of definite conducting paths, any provision on the part of the 

 adjacent ribs and anastomoses does not take place. In leaves of 

 the beech the helmet.*like galls of Hormomyia fagi (compare fig. 

 58) which are produced on the side or midribs are often found 

 very abundantly. The part of the blade provided for by the rib 

 bearing the gall always bleaches very noticeably above the gall. 

 If the gall is on a aide rib, bleached stripes are produced; if 

 on the main rib, a pale green, rhoraboidal field is produced at 

 the tip of the leaf,- a proof that the intact adjacent ribs and 

 anastomoses are not in condition to provide slifficiently for th3 

 areas lying above the gall. 



