664 METHODS OF SPECIAL STAINING ETC. 



fied by some with mitochondria. Zirkle {Bot. Gaz., Ixxxviii, 

 1929, p. 186) defines as mitochondria all small inclusions preserved 

 by bichromates with a pH greater than 4-2 to 5-2 (dependent on 

 the cation) and destroyed by more acid bichromates and by 

 mixtures of bichromates and acetates ; he restricts the term 

 " plastid " to those bodies containing starch or chlorophyll. He 

 fixes plastids and their primordia in 1-25 grm. potassium bichro- 

 mate, 1-25 grm. ammonium bichromate, 1 grm. copper sulphate 

 and 100 c.c. water. 



The mitochondria and the pro-plastids appear to react 

 differently to impregnation (see Bowen, Zeits. Zellf. Mikr. Andt., 

 vi, 1929, p. 689) and have a different appearance and behaviour 

 in tissues affected with mosaic (Dufrenoy, Rev. Path. Veg. 

 Entom. Agr., xviii, 1931, p. 74). But Ozawa {Rev. Gen. Bot., 

 xxxix, 1927, p. 218) finds that plastids, proplastids and mito- 

 chondria react similarly. 



The mitochondria are best seen by Champy-Kull, the plastids 

 by Weigl and in Benda preparations. 



A few special methods and modifications of animal methods 

 have been suggested. 



1330. Mitochondria are preserved by neutral formalin ; fix 

 forty-eight hours, wash in water and stain in Heidenhain's haema- 

 toxylin. Mottier {Ann. Bot., xxxii, 1918, p. 91) finds a mixture 

 of 17 c.c. 1 per cent, chromic acid, 3 c.c. 2 per cent, osmic acid 

 and 3 drops acetic acid the best fixative. 



See also Zirkle, Science, Ixvi, 1927, p. 400. 



Ozawa {Rev. Gen. Bot., xxxix, 1927, p. 218) states that Regaud 

 (without post-chroming), Tupa and Helly are most satisfactory, 

 and that all other mitochondrial fixatives, especially those con- 

 taining osmic, produce marked alterations. He used the bud of 

 Elodea canadensis. According to Bowen, the Champy-Kull 

 method is practically specific. Levitsky {Ber. Deuts. bot. Ges., 

 xxviii, 1910, p. 540) used a mixture of 8-5 parts of 10 per cent, 

 formalin and 1-5 parts of 1 per cent, chromic acid, followed by 

 treatment with Benda. The formalin-chromic alone, was less 

 satisfactory since staining became more difficult. 



Lenoir {Rev. Gen. Bot., xxxviii, 1926, p. 720) uses a mixture of 

 equal parts of 2 per cent. KI and 2 per cent, chromic acid. This 

 rapidly fixes and stains the mitochondria in epidermal cells of 

 Allium cepa. 



Mascre (C R. Acad. Sci., clxxxv, 1927, p. 866 ; clxxxviii, 

 1929, p. 811) states that a preliminary treatment with formal- 

 dehyde protects the mitochondria from the solvent action of acetic 

 acid. He finds that monochloracetic, trichloracetic and cyanacetic 

 acids fix the mitochondria, but treatment with formalin is essential 

 to prevent subsequent solution in the rinse water. He uses the 

 following mixtures ; — - 



