Special Methods 135 



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 diffi- 

 culty. 



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. 



