STAINING VEGETABLE TISSUES. 241 



the sections appear sufficiently coloured a dark blue, 

 transfer them once more to a saucer of water to which a 

 drop of an aqueous saturated solution of arsenious acid, 

 or of oxalic acid (in the proportion of one grain of oxalic 

 acid to the ounce of water) or glacial acetic acid has 

 been added. Wash by rotating the saucer, then pour 

 off the water and place the sections in a stoppered 

 bottle containing absolute alcohol ; which should like- 

 wise contain a drop of either of the before-mentioned 

 acids. When all the water has been abstracted from 

 the sections by the alcohol (which will be in about ten 

 minutes) clear with oil of cloves, they are then quite 

 readv for mounting in Klein's' or dammar solution. 

 Clematis and other open sections take a very fine treble 

 stain by this method. Buckthorn and sycamore seem 

 to have a great affinity for the green stains, two minutes 

 in staining fluids being usually sufficient to colour the 

 walls of the central cells green and their contents of a 

 light scarlet. The staining of thin sections of potato 

 are equally effective, the starch granules being green, 

 the loculi scarlet, the depth of colour depending upon 

 the length of exposure to the atlas- scarlet, and mixed 

 green dyes; always allowing the malachite to be in 

 excess. 1 



For double-stained vegetable tissues Mr. Barrett 

 prefers some of the cheaper dyes. The sections must 

 be first immersed in an aqueous one per cent, solution 

 of Crawshaw's aniline blue; then removed into a 

 strong acetic acid solution, which fixes the colour in 

 certain tissues, and removes it from others, while it 

 prepares the unstained portion for the reception of 

 another colouring material. It must again be removed 

 into a weak solution of magenta (Judson's dye), acidu- 

 lated with acetic acid : then washed and mounted in 

 glycerine jelly. By this process sections of burdock are 

 stained, the pith, very pale magenta colour; cellular 

 tissue, deep magenta ; spiral vessels of medullary sheath, 

 deep blue ; pitted vessels, blue ; cambium, deep blue ; 

 liber cells, dark magenta ; lactiferous vessels, deep 

 blue ; cuticle, parenchyma, pale blue ; epidermis, deep 



(1) Transactio-M of the Uoral Microscopical Soe., page 870, 1881. 



