Smithsonian Report. 1940. — Weintraub 



PLATE 3 



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1 . Cultures of Tobacco Callus Cultivated in Vitro From (Extreme Left) 

 TO 10 Weeks (Extreme Right). 



Courtesy of Dr. P. R. White (Amor. Journ. Bot., February 19.39). 



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2. Transverse Section Through Central Part of an 8-Weeks-Old Callus 



Culture. 

 Courtesy of Dr. P. R. White (Amer. Journ. Bot., February 1939). 



3. Callus Cultures. 



Left, callus cultured for 20 weeks on a semisolid agar medium; right, a similar culture grown for 10 weeks 

 on the agar medium, then transferred for 10 weeks to a liquid medimn containing the same nutrient 

 materials but without the agar. Courtesy of Dr. P. R. White (Bull. Torrey Bot. Club, November 

 1939). 



