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METHODS IN PLANT HISTOLOGY 
the usual display of vacuoles and which appears before any vacuoles 
can be recognized in preparations made in the usual way (Fig. 28 B). 
Being a zoologist, he has called these vacuoles “canaliculi.” 
VASCULAR BUNDLES IN LIVING TISSUES 
In studying venation, and in tracing the course of vascular 
bundles in large ovules and in other organs, it is often an advantage 
to use a stain. If a stem of Impatiens be cut under water, and the 
cut surface be then placed in a dilute aqueous solution of eosin, the 
eosin will rise in the vessels, making them very prominent. The 
outer bundles of the large ovules of cycads are very easily studied 
by this method. The inner bundles also may be seen by opening 
the seed and removing the endosperm. 
If such preparations could only be cleared, they would be still 
more valuable, but the effect is due to the presence of the staining 
fluid in the vessels, and any subsequent treatment diffuses or destroys 
the stain. Perhaps a little experimenting might obviate the difficulty. 
STAINING LIVING STRUCTURES 
Some stains will stain living structures. Cyanin, methyl blue, 
and Bismarck brown have been recommended for this purpose. The 
solutions should be very dilute, not stronger than 1:10,000 or 
1:500,000. The solutions should be very slightly alkaline, never 
acid. It is claimed that such solutions never stain the nucleus, and 
that if the nucleus stains at all, it is an indication that death is taking 
place. 
Campbell succeeded in staining the living nuclei in the stamen 
hairs of Tradescantia by using dilute solutions of dahlia and of 
methyl violet (0.001 to 0.002 per cent in water). Dividing nuclei 
were stained. 
For determining the stage of development of fresh material it is 
often necessary to use a stain. For this purpose stronger stains may 
be used, since it is unimportant whether the tissue is killed or not. 
An aqueous solution of methyl green or eosin can be recommended. 
With 1 per cent solutions, diluted one-half with water, mitotic 
figures can be recognized with ease. 
