OF SAP IN PLANTS. 5 



places where the laxity of the tissue and the direction of the 

 cells oppose the smallest amount of resistance ; just as in blotting 

 or other unsized paper. 



2. Lichens. 



Cladonia subulata t Wallr. The lumps of earth on which the 

 plant grew were placed in the test fluid, and the whole was 

 covered with a plate of g ] ass, in order to maintain a moist atmo- 

 sphere. Yet even after ten days the plant was not permeated 

 throughout ; it had become coloured blue in some places, which 

 indicated a natural existence of salts of oxide of iron in it. After 

 the application of chloride of iron, moreover, to various sections, 

 only a slightly deeper blue colour presented itself, which is 

 readily explained by the extraordinary density of the tissue, and 

 the consequent slow conduction of the juices in the lichen, which 

 is itself of a rather dry nature. The blue colouring was uniform, 

 and exhibited no marked limits. 



3. Mosses. 



Syntrichia ruralis. The moss and the soil supporting it were 

 so placed in the fluid that the former remained unwetted ; the 

 atmosphere was kept damp as above. The stem conveyed the 

 fluid upwards ; the leaves exhibited an uniform blue colouring 

 at the base, which however spread very slowly over the surface, 

 when the chloride of iron was dropped upon them ; the fluid 

 advanced much more rapidly towards the point in a row of cells 

 lying close beside the margin, while the mid-nerve acquired no 

 perceptible colour. The chlorophyll granules did not seem to 

 exert any especial influence on this conduction, since the lowest 

 cells appeared coloured uniformly blue, in spite of their total 

 absence. In the cells lying somewhat higher up, the blue colour 

 did indeed correspond with the heaps of chlorophyll, which was 

 perhaps only an optical phenomenon : further up the cells were 

 pure green. 



Barbula muralis^ Timm. Treated as above : half mature, like 

 the foregoing. Here again a blue stripe of more delicate cells 

 was seen along the margin up to the apex, after the application 

 of the reagent, while no discoloration could be detected in the 

 mid-nerve, and on the general surface of the parenchyma of the 

 leaf only isolated spots occurred, appearing to indicate a very 



