THE USE OF POLARIZED LIGHT IN VEGETABLE HISTOLOGY. 297 
plate, through the interposed object in its doubly refracted wall- 
parts, rises to blue or sinks to yellow, and where the shifting of the 
Miiller’s band to red or blue takes place), show the cambium-wall 
as a stripe, shining in the respective colours, between the strongly 
darkened, almost black, primary walls. 
In the second preparation (longitudinal section through the seed- 
albumen of Phytelephas macrocarpa), we select such a suitable spot 
that, in the red-coloured field of view, in the usual experimental 
arrangement for polarized light, the aforesaid colour-phenomena, 
which indicate the change of the ellipsoid of elasticity, stand out 
the finest, and we observe at this spot the appearances in the 
spectrally-dissected polarized light ; then we find the most decided 
and undoubted evidence in the inner layer of the change in the 
direction of the two effective axes of elasticity. We have arranged 
the optical part of the spectro-polarizer as suggested in the “‘ Hand- 
buch der allgemeine Mikroskopie,” p. 984, whereby the greater axis 
of elasticity runs parallel to the ends, the smaller parallel to the 
side of the object-slide ; and we now insert the section of the longi- 
tudinal wall lying between two neighbouring illuminated cells, over 
Miiller’s band, when the collective wall-layers, consisting of cell- 
substance, whatever course they may take, appear in green. We 
push this wall towards the red of the spectrum, when the wall- 
layers appear running together parallel to the long axis (and there- 
fore to the ends of the object-slide), in which layers the greatest 
axis of elasticity of the flat section is arranged in the same way as 
the same axis would be by means of the selenite-plate, somewhat 
obscured in the orange ; whilst the inner layer, so far as it reveals 
the pore-canal, is brightly lighted, and thereby informs us that in 
this same spot, in which the effect of the axes of elasticity takes 
place, the less axis is arranged by the selenite in a direction con- 
trary to that of the greater, and therefore assumes a position in 
the section of the ellipsoid of elasticity approaching to go” to the 
part running lengthwise. When the movement is made towards 
the other end of the spectrum, the appearance is reversed, an 
obscuration of the revealed inner layer of the pore-canal takes 
place in the blue, between Fraunhofer’s lines F and G, whilst the 
wall-layers running in the direction of the long axis leave the con- 
nected colour-region in unchanged brightness. 
Some further observations in polarized and spectrally-dissected 
light, especially in reference to the change or persistence of the 
degree of double refraction under various circumstances, and upon 
the question whether double refraction of the cell-walls, of the 
starch-granulations, &c., may depend upon tension-relations or 
upon differences of molecular constitution, shall be reported in 
another communication, because I am now occupied in appropriate 
researches. 
