196 SECTIONAL ADDRESSES. 



rounded with a saturated atmosphere. Neglect of these facts led Czapek 

 into error. Deleano also showed that organic substances continue to 

 leave the blades even after the petioles have been killed by heat or by 

 chloroform-vapour. The rate of depletion is reduced by the foiTner 

 agent to about one-third, and by the latter to one-half. If this observa- 

 tion is substantiated it would show that the intervention of living 

 elements is not essential for the transport. He further found that the 

 blades attached to petioles which were surrounded by chloroform-water 

 lost their starch more quickly than those immersed in water. 



The contradictory conclusions of Czapek and Deleano urgently call 

 for a reinvestigation of the points at issue. It is not enough to assume, 

 as Schrooder does, a completely sceptical attitude towards the latter 

 investigator's account of his experiments. If Czapek's work holds good, 

 we shall have to regard the bast, and especially the sieve-tubes, as the 

 channels for the transport of organic substances back from the leaf- 

 blades where they are manufactured, and we must look for some hitherto 

 undreamed-of method of transmission through these most unlikely- 

 looking conduits. On the other hand, if Deleano 's conclusions are 

 borne out, we should admit that protoplasm is not necessary for the 

 transport, and we shall turn to a dead tissue as furnishing this channel. 



So far as I am aware none of the earlier investigators made any 

 estimate either of the actual quantities of organic material which are 

 transported or of the velocities of flow in the channels which are 

 necessary to effect this transport. 



We may approach this problem from two opposite directions — (1) by 

 dealing with the amount of organic substance accumulated in a given 

 time in a storage organ, or (2) by using the amount exported from an 

 assimilating organ. The cross-section of the supposed channels of 

 transport and the volume of the solution containing the substances in 

 each case will give us the other necessary data. 



For the first method a potato-tuber will furnish an example. One 

 weighing 210g. was found attached to the base of a plant by a slender 

 branch about 0.16cm. in diameter. In this branch the bast had. a 

 total cross-section of 0.0042cm.2. This figure is a maximum ; no 

 allowance was made for the cross-section of the cell-walls, or for any 

 non-functional elements in the bast. The cell-walls would occupy 

 probably one-fifth of the cross-section of the bast. Now if the bast 

 exclusively furnished the channel of downward transport, all the 

 organic substance- in the potato must have passed this cross-section 

 during the time occupied in the growth of the potato. One hundred 

 days would be a liberal allowance. According to analyses more than 

 24 per cent, by weight of the potato is combustible. Therefore we must 

 assume that during this time more than 50g. of carbohydrate has 

 passed down a conduit having' a cross-section of no more than 

 0.0042cm.-. The average concentration of the solution carrying this 

 substance could scarcely have been as much as 10 per cent. (2.5-5 per 

 cent, would be more probable. The concentration of sugar 

 in bleeding sap is much below this figure, and seems never to reach 

 4 per cent.). Assuming, however, this concentration, the volume of 

 liquid couAeying 50g. must have been 500cm.'', and this quantity must 



