761 



I( appeal's then, thai here also the vellow leaves suffer under a 

 deficiency of suction force, and nnder circumstances hronght about 

 by stronger evaporation are sooner destroyed tlian the green ones, 

 althougli the hitter evaporate comparatively more intensely. 



With partially I'iiiged variegated shoots the midsummer growth 

 occurred also at the top. With completely ringed specimens, however, 

 it appeared be.Iow the surface of the wound from lateral or dormant 

 buds. (See photo). This occurred as well when the surface of the 

 wound was covered with butter of cocoa, as when it was dressed 

 witli a water-bandage. 



The check to the food-supply is apparently as great with Aesculus 

 as with Acer Negundo, in spite of the greatest |)recaution used in 

 cutting the ring. It follows, then, that the experinnents do not yield 

 any evidence whatever, to lend support to Dixon's theory. They 

 rather go against it. 



Still conclusive evidence to disprove Dixon's theory cannot be 

 brought forward by this procedure, since in spite of all due precau- 

 tion the |)eripheral wood may be prevented by tlie ringing from 

 perfoiming its function, as far as the transport of the organic 

 products is concerned. 



With regard to other inquiries, whose results tell strongly against 

 Dixon's theory, we first of all have to think of Hanstkin's experi- 

 ments (I.e.) on the root-growth of ringed branches in water culture. 



Hanstein finds that detached branches placed in water send out 

 roots chiefly at the basal extremity of the stem, which Vochtino 

 ascribes to the polarity of the parts. Leafless branches when ringed 

 ilevelop a large number of roots just above the wound; whether 

 and to what number they will grow at the bottom of the bianch, 

 depends on the distance between that extremity and the ringing. 



Hanstkin ascribed this to the check to the transport of nutriment 

 consequent on the removal of the phloem, and established, indeed, in 

 such circumstances a distinct difference in the root-growth, between 

 dicotyledonous plants with an anomalous stem-structui'e and those 

 with a normal stem-structure, in which the stem derived its thick- 

 ness form a ring of collateral vascular bundles. With the former 

 the transport of carbohydrates and proteins is believed to be only 

 partially checked. This is ascribed to the fact that the vascular 

 bundles are contained within the xylem (as Avith Piperaceae and 

 Nyclaginacea) or (as in the case of Apocynacea and some Solanacea) 

 to the fact that there are originally bicollateral vascular bundles or 

 rather medullary phloem strands and consequently phloem remains 

 also within the secondary xylem. Owing to this Hanstein stated 



50 



Pnxeediiijfh t-!i)yal Aoad. Amsleidaiii Vol XXVI. 



