464 SCIENCE PROGRESS 



portant thing to be examined, and Schimper's account of this 

 is here quite inadequate. The disappearance of starch from 

 mesophyll is not by itself a satisfactory indication of the 

 amount of sugar translocated from the leaf, for as Sachs 

 showed in the case of cut leaves a considerable loss may be 

 due merely to translocation into the larger veins. Moreover 

 during ten warm days respiration must have caused a con- 

 siderable diminution in the amount of starch and sugar present 

 in the leaves, quite apart from translocation. 



Czapek was of the opinion that while Schimper's experi- 

 ment showed that the sugars could pass from the mesophyll 

 into the " Leitscheide," it was quite another question whether 

 they left the leaf by this path or by another in the normal 

 course of events. 



Numerous ringing experiments have also been carried out 

 on plants possessing a laticiferous system with results of 

 considerable interest. 



As mentioned above, Hanstein found that ringed twigs of 

 dicotyledonous plants having bicollateral bundles (phloem both 

 external and internal to the wood) behave differently from 

 those with collateral bundles (phloem only external to the 

 wood), as far as the production of roots is concerned. He 

 thought therefore that if laticiferous tubes could take the place 

 of the phloem in conducting nutriment, ringed twigs with 

 collateral bundles and laticiferous tubes in the pith should 

 behave like ringed twigs having bicollateral bundles. 



However, experiments with twigs of Ficus Carica (which 

 has medullary laticiferous tubes) showed that only a very 

 poor development of roots took place below the ringing, so 

 that a sufficient supply of nutriment could not have been 

 forwarded by the laticiferous tubes in the pith. 



In 1905 Kniep obtained a similar result with Ficus australis 

 which also has medullary tubes. Hanstein performed another 

 experiment upon this species of Ficus. A ring of tissue was 

 removed from a twig just beneath the growing end, and the 

 leaves already formed above it were plucked. The upper 

 part of the twig died, which he thought would scarcely have 

 happened if it had been able to obtain nutriment from the 

 assimilating part below the ringing for the unfolding of new 

 leaves. 



