460 BOTANICAL GAZETTE [JUNE 
An extremely satisfactory stain for photographic purposes is the 
iron-alum haematoxylin of Heidenhain. The method with this stain 
is given in full by Chamberlain. We find it desirable to wash the 
sections repeatedly in distilled water after using the iron-alum, before 
placing them in the haematoxylin. This stain is especially useful in 
the study of wood sections. A contrast stain of safranin may be added 
if desired, but it is of doubtful value for practical purposes. 
It frequently happens, as in sectioning buds, ovaries, etc., that it is 
necessary to preserve the celloidin matrix of the section in order to 
prevent displacement of the otherwise separate parts of the section. 
In this case the sections are transferred directly from go per cent. 
alcohol to water, and are stained as usual. Dehydrate in a mixture of 
absolute alcohol and chloroform, clear and mount. The chloroform 
counteracts the solvent action of the absolute alcohol, and preserves 
the celloidin film perfectly. 
VII. Sertal sectioning.—In order to make serial mounts by the cel- 
loidin method, the sections are cut in the following mixture, instead of 
in 90 per cent. alcohol: go per cent. alcohol 85 parts, glycerin 15 
parts. As the sections are cut they are to be arranged on a piece of 
smooth, thin paper. As soon as the alcohol has evaporated from the 
sections, turn the slip of paper face down upon a slide which has been 
coated with albumen fixative,add several layers of paper, and press the 
whole firmly down upon the slide by means of a photographic squeegee 
roller; then put another slide on top of the layers of paper, clamp 
all together by suitable spring clips, and place in the paraffin bath 
to dry for not more than twelve hours. A longer time than this 
renders the celloidin more or less insoluble. The paper may now 
be stripped off, leaving the sections firmly attached to the slide. Pass 
the slide through alcohol, ether, alcohol, stain, etc., as with separate 
sections. 
The most important steps in this method are desilicification and 
dehydration of the material. With due attention to these points, and 
with a proper allowance of time for infiltration, the hardest tissues 
may be put in perfect condition for sectioning. 
The method is found to be of special value wherever it is desirable 
to reproduce with absolute fidelity by means of photomicrography the 
appearance of skeletal and other hard tissues of plants. The greatest 
usefulness of the method, however, is in connection with the teaching 
of morphology and histology, insuring as it does the absolute uni- 
3 CHAMBERLAIN, C. J., Methods in plant histology, Pye tas 
