VAEIATIONS IN DATURA DUE TO CHANGES IN 

 CHROMOSOME NUMBER 



DR. ALBERT FRANCIS BLAKESLEE 

 Station for Experimental Evolution, Cold Spring 

 Harbor, L. I., N. Y. 



Two forms with which we have recently carried on 

 breeding experiments, the garden flower Portulaca and 

 the jimson weed {Datura Stramonium) , are strikingly- 

 different in the types of variations which they show. 

 The Portulaca is procurable in a wide range of color va- 

 rieties, and is apparently subject to relatively frequent 

 mutations, both seminal and somatic, with sectorial and 

 periclinal chimeras a. common phenomenon. Sufficient 

 breeding tests have been made to indicate that the varie- 

 ties of Portulaca are due in large measure at least to gene 

 mutations. In comparison with Portulaca, the jimson 

 weed is relatively stable so far as gene mutations are 

 concerned. Despite the large amount of breeding work 

 with this species, both before and since the rediscovery of 

 Mendel's law, only the two allelomorphic pairs of char- 

 acters, purple vs. white flowers, and spiny vs. smooth cap- 

 sules, have been identified aside from the pair, tall vs. 

 short stature recently determined by the writer and 

 Avery (3). 



It is true that certain of our pure lines of Datura differ 

 slightly from others when grown in comparable pedi- 

 grees, but the fact remains that so far as sharply con- 

 trasting Mendelian characters are concerned, the jimson 

 weed is highly stable, while the Portulaca is highly mu- 

 table. Our knowledge of changes in chromosome number 

 in other forms is not sufficient to indicate if there is any 

 significance for the present discussion in the difference 

 just mentioned between Portulaca and Datura. 



Our interest in Datura began about 1910 or 1911, when 

 the jimsons were used as demonstration material for 

 students in genetics. In 1915 we found our first mutant 

 which we called the Globe from the shape of its capsules. 

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