K.— BOTANY. 195 



also duiitig summer growth an up\\'ard transport of carbohydrates in 

 the water tracts occurs. 



This view that the channel for the backward and downward move- 

 ment of organic substances is afforded by the bast received great sup- 

 port from Czapek's work published in 1897. By section of the con- 

 ducting tracts in one half of the petiole he showed tliat depletion of 

 the corresponding half of the blade was delayed. He also showed 

 that only where vertical bridges connected the upper and lower portions 

 of bark in ringed stems were the effects of ringing nullified. Oblique 

 and zigzag bridges are ineffective. Thus transverse conveyance in the 

 stem is negligible. The parallel and longitudinal arrangement of the 

 elongated elements in the bast seemed to him to provide adequately for 

 the observed longitudinal passage. Their nari'owness and large colloid 

 content did not present themselves as difficulties. 



He also recorded the observation that the blades of leaves, the 

 petioles of which had been killed by jacketing them with steam, did 

 not become emptied of starch. Similarly, when the petioles were killed 

 with chloroform-vapour, depletion was arrested. Again, anaesthetisa- 

 tion of the petiole, by surrounding it with a watery solution of chloro- 

 form, greatly delayed the disappearance of starch. On the other hand, 

 depletion was not obstructed when the petiole was immersed in a 5 per 

 cent, solution of potassium nitrate. From this last observation he con- 

 cluded that plasmolysis of the translocating elements does not interfere 

 with their function as channels of transport. 



Czapek formed no definite theory as to how organic substances were 

 moved in the bast. He was sure that the transport depends on living 

 protoplasm. He did not consider that the streaming of protoplasm 

 contributed materially to the motion, seeing that streaming does not 

 occur in mature sieve-tubes. He regarded the sieve-tubes as the most 

 important elements in the transmission of these substances, because the 

 deposition of callus in the sieve-plates synchronises with the stoppage 

 of transport. The transport, according to him, is not simply due to 

 diffusion. He supposed the protoplasm to take up the organic sub- 

 stances and pass them on. If diffusion does not account for the passage 

 from one particle of protoplasm to the next, it would seem that we 

 must suppose the organic substance to he pix>jected from one to the 

 other. 



These observations and their interpretation by Czapek have 

 strengthened the opinion that the bast is the channel for the downward 

 transport of organic substances. It is remarkable how little weight has 

 been attached to the damaging criticism of Czapek's views by Deleano, 

 especially as those views are so unsatisfactoiy from a physical stand- 

 point. 



The latter author showed that it is inadmissible to compare externally 

 similar leaves, which often behave, so far as depletion is concerned, 

 very dissimilarly. He also pointed out that without any export a 

 leaf may be depleted of all its starch within thirty-five hours, and 

 partially anticipated an extremely interesting recent observation of 

 Molisch — namely, that transpiring leaves lose their carbohydrates much 

 more rapidly than those whose transpiration is checked by being sur- 



