756 



On the one side Otis Curtis') made single and doul)le ringing 

 experiments and arrived at the conclusion tiiat the transport of 

 carbohydrates and |)r()teins lo the shooting parts may occur throngii 

 the secondary phloem just as well as the transport in the opposite 

 direction does, when ihe surplus of assimilates is removed from the 

 place of formation. In my judgment, however, his view has not 

 been sufiiciently reinforced by indispensable quantitative examination. 



On the other side it is Atkins') and Dixon") in England, and 

 LciSK BiKCii lIiHsnii'Ei.n *) in Germany who deny almost any signi- 

 ticance to the phloem for the malter-transport. Their arguments 

 consist in the main of indirect evidence. Atkins argues ihat Ihe 

 bleeding saps are more or less rich in car'bohydrates not only in 

 spring but also in other seasons. Llisk Biuni HiiiCHFKi.i) and after- 

 wards Dixon base their most cogent argumeiils upon their lielief 

 thai an adecpiate transport of matter along the phloem can hardly 

 be presumed. This difficulty had already been obviated i)y Hroo de 

 Vkies"), who made a- (|uicker transport than the law of diffusion 

 admits conceivable by assuming protoplasm-slreams in the |)hloem- 

 elemenls. Dixos, however, considers Ihe impossibility of a transport 

 of adecpiate capacity along the phloem as conclusive evidence for 

 denying any significance to the phloem in this respect. Hikch Hihschfki,d 

 is less positive in her assertion. 



That, beside an ascending stieam in the wood, there may also 

 be a coinciding transport along it towards the bottom of the stem, 

 may be concluded from various investigations i.a. Ihe above-named 

 by L. Hiiicii IIiKSCHFEi.i). Then the rate of transport can be much 

 (juicker than in the phloem and Ihe capacity of the conducting 

 channels can likewise be greater, as it is a fact that the phloem- 

 produclion of cambium is invariably smaller than that oflhexylem, 

 while the generated |)hloem is obliterated much sooner. 



This conce|)tion of Dixon's, however, does not square with the 

 result of the ringing experiments of Hanstein, which result points 

 indubitably to the stream of assimilates being stopped when Ihe 

 ringing wound is made deep enough to reach Ihe cambium. Dixon 

 therefore assumes the transport to [)ass through the youngest parts 

 of the secondary xylem, which parts being located close to the 

 cambium, are l)y him believed to be injured and thus rendered 

 inactive by the ringing. 



I) Otis F. Curtis. American Journal of Botany, 1920. 



•^) W. R. G. Atkins. Some recent researches in Plant Physiology, 1916. 



S) H. H. Dixon, Pies. Address. Bot. Society, 1922. 



*) L. Birch Hirschfeld, Jahrb. f. wiss. Botanik, 1920. 



5) Hugo de Vries, Bol. Ztg., 1885. 



