26 TRANSPIRATION AND ASCENT OF SAP ch. 



casts of the vessels streaming upwards from below like a 

 sheaf of fine white threads. The examination of these 

 threads under the microscope reveals many features of 

 interest. Figs. 5, 6 and 7 represent portions of some 

 of these casts. 



Some further experiments were made bearing upon the 

 ascent of water in the wall. All confirm the fact that an 

 appreciable quantity of water ascends in branches most 

 carefully choked with paraffin. 



Thus, while flagging will inevitably overtake a paraffined 

 branch left furnished with the same number of leaves as 

 it bore upon the tree, yet if the greater number of these are 

 removed, the remaining leaves will generally hold out fairly 

 well. This experiment was tried with a control paraffined 

 branch upon which all the leaves were left standing. 



If after injection we remove part of the branch at a fork 

 and, keeping the one part which is attached to the 

 paraffined extremity in water, insert the extremity of the 

 other through a cork into a dry vessel, the latter will flag 

 much the more rapidly. Still more direct is the following : a 

 paraffin-injected branch of Tilia micropkylla, with nine 

 leaves, was put standing, from 4.15 p.m., May 11, till noon 

 on the 12th, in a vessel of water which had been carefully 

 weighed and so closely corked round the stem as to preclude 

 possibility of loss by evaporation at its surface. In this 

 period of nearly twenty hours the branch drew up 1*005 

 grammes of water. This same branch, after it had flagged, 

 and had been put out into breeze and intermittent 

 sunshine from noon till 3.30 p.m., drew up 0*161 gramme. 



Again, of two paraffin-injected lime branches, one 

 scraped to free the surface and placed in water, the other 

 left closed with its cap of solid paraffin ; the latter flagged 

 much more quickly, although it bore a smaller number of 

 leaves. In two days the second was, indeed, dry and 

 shrivelled, while the former had preserved much of the 

 freshness of its leaves. 



