270 Methods in Plant Histology 



Osterhout 1 experimented with forty fixing agents, and then con- 

 cluded that Flemming's stronger solution was the best. Professor 

 Gregoire and his students have made this their principal fixing agent. 

 In spite of the weight of authority, we believe that the value of 

 solutions with such a large proportion of osmic acid has been over- 

 estimated. Some osmic acid is, doubtless, desirable, but we should use 

 only half the amount of osmic recommended in Flemming's weaker 

 solution. The formula for that solution is often given as follows: 



[ Chromic acid (1 per cent) 25 c.c. 



A | Glacial acetic acid (1 per cent) 10 c.c. 



{ Water 55 c.c. 



B. Osmic acid (1 per cent) 10 c.c. 



Keep the mixture A made up, and add B as the reagent is needed 

 for use, since the solution does not keep well. One seldom uses this 

 reagent in large quantities. About 40 c.c. is as much as one is likely 

 to need for any collection of anthers or root-tips. Take 36 c.c. of A 

 and 4 c.c. of B. It will be worth while to try 36 c.c. of A and 2 c.c. 

 of B, or even 1 c.c. of B. If the regular formula is used, we should 

 let it act for an hour, and then replace it by A, without any osmic 

 acid. The osmic acid undoubtedly accelerates the killing of the 

 protoplasm. This is seen more readily in animals. If Cyclops be 

 brought into 30 c.c. of the solution A, the animals will swim for 

 awhile; if 5 or 6 drops of 1 per cent osmic acid be added to the 

 solution, the animals cease their movements almost instantly. 

 Doubtless the osmic acid has the same effect upon plant protoplasm. 

 Where fixing is slow, very few mitotic figures are found with the 

 chromosomes midway between the equator and the poles. The 

 addition of 10 drops of 1 per cent osmic acid to 50 c.c. of the solution 

 just mentioned will secure as large a proportion of anaphases as 

 solutions which are stronger in osmic acid, and there is no disagreeable 

 blackening. 



Farmer and Shove, 2 in studying these mitoses and also vegeta- 

 tive mitoses in Tradescantia, secured better results with a mixture 



1 Osterhout, W. J. V., "Cell Studies, I, Spindle Formation in Agave," Proc. Cal. 

 Acad. Sci. Botany, Third. Series, 2:255-284, 1902. 



2 Farmer, J. B., and Shove, Dorothy, "On the Structure and Development of the 

 Somatic and Heterotype Chromosomes of Tradescantia virginica," Quart. Jour. Mic. Sci. 

 48:559-569, 1905. 



