98 
METHODS IN PLANT HISTOLOGY 
cover. Dip the brush in the balsam again, and gradually extend 
the ring until it is about tV inch wide on the cover. The touch must 
be extremely gentle or the cover will be moved. Do not try to put 
on a thick ring the first time, but let a thin ring harden for an hour 
(months would do no damage), and then a thicker ring can be added 
without any danger. Thin rings are too likely to be broken, and 
thick rings are in the way if the preparation is to be examined with 
high powers. A medium ring is best, and it should consist of two 
coats, for a crack would seldom appear at the same place in both 
coats. A good shape and thickness for a ring are shown in Figure 20. 
I- ~~ - 1 
Fig. 20.—Slide, natural size, showing size and form of the ring 
The following is a summary of the foregoing processes: 
1. Fix in chromo-acetic-osmic acid, 24 to 48 hours. 
2. Wash in water, 24 hours. 
3. Iron solution, 2 hours. 
4. Wash in water, 10 minutes. 
5. ^ per cent haematoxylin, 3 to 24 hours. 
6. Wash in water, 10 minutes. 
7. Iron solution until stain is right. 
8. Wash in water, 1 hour. 
9. 10 per cent glycerin. 
10. Mount and seal. 
If the material has been fixed in formalin, it should be washed in 
water for 5 to 10 minutes before staining. Material preserved in 
70 per cent alcohol should be placed successively in 50 per cent, 35 per 
cent, 15 per cent alcohol, and then in water, allowing each to act 
for 15 to 30 minutes before being placed in the stain. 
Mayer’s haem-alum is also a good stain for filamentous algae and 
fungi which are to be mounted in glycerin. The process, after fixing 
and washing in water, is as follows: 
1. Transfer to the stain from water. 
It is seldom necessary to stain longer than 10 minutes. As a 
rule, it is better to dilute the stain (about 1 c.c. to 10 c.c. of distilled 
water) and allow it to act for 10 hours or over night. 
2. Wash in water, 20 minutes. 
3. 10 per cent glycerin until sufficiently concentrated. 
4. Mount and seal. 
