358 



Mr F. Darwin and Mr R W. Phillips, [Nov. 23, 



It will be seen that the difference pointed out between the 

 transpiration- and filtration-streams is quite in accordance with 

 the intracellular theory of water transport, though it may also 

 perhaps be consistent with what we know of imbibition. 



§ 7. Experiments with solution of eosin and with ivater containing 

 coloured particles in suspension. 



The adherents of the inhibition theory naturally look with 

 suspicion on experiments made with coloured fluids, but to others 

 they are not without interest. 



If a transpiring branch be placed in a solution of eosin, the 

 colour as is well known gradually spreads over the whole speci- 

 men, so that the leaves become discoloured and the wood of the 

 smallest twigs shows a bright pink colour. But if the branch 

 has been doubly sawn before it is placed in the eosin a very 

 characteristic appearance is produced. Fig. 3 is a diagram re- 

 presenting the appearance of such a branch. Above the "double 

 saws " the colour shows in two narrow strips running close behind 

 the uppermost saw-cuts, that on the side nearer to the observer 

 being shown at a. Below the two saw-cuts is a strip of tissue b 

 corresponding to a; this spreads out until lower down at a point not 

 shown in the diagram the whole branch has become coloured. 

 Between the saw-cuts is a belt of colour marked by a horizontal 

 arrow which unites the streams a and b. 



The more usual appearance is shown in fig. 4 where the colour 

 is fairly spread over the whole surface of the branch below the 

 lower cut, but where above the upper saw-cut the two strips a, a, 

 are seen. In a transverse section these two streams may be seen 

 as two wedge-shaped areas of colour. 



The course of the stream may also be shown in another way. 

 If the cut end of a transpiring branch be immersed in water 

 containing coloured particles in suspension, the cut surface rapidly 

 assumes a bright tint of the colour employed. 



