A GRAFT-INFECTIOUS DISEASE OF DATURA 

 RESEMBLING A VEGETATIVE MUTATION. 



By a. F. BLAKESLEE, 

 Station for Experimental Evolution, Cold Spring Harbor, N.Y. 



(Received May 15. 1920.) 



(With Plates II— VI.) 



I. Introduction. 



At the New York meeting of the Botanical Society of America in 

 1916 the writer presented a paper entitled "A Recurrent Mutation in 

 Datura Suggesting Vegetative Segregation." As reported at the next 

 meeting of the Society, more recent experiments have shown that the 

 peculiarity is in the nature of a disease since it can be transmitted by 

 grafting upon normal stock. The variation involved, among changes in 

 other morphological characters, a suppression of spines on the capsules. 

 As observed by earlier geneticists, it had been assumed to have resulted 

 from imperfect dominance of spininess when the normal type was 

 crossed with a smooth-capsuled variety. In as much as the disease is 

 transmitted through both seed and pollen and causes profound mor- 

 phological changes in the individuals affected, it at first appeared to 

 be genetic in nature. It seems appropriate therefore to publish the 

 present paper in a journal of Genetics rather than in one devoted to 

 phytopathology with the thought that results obtained in Datura may 

 be of possible value to geneticists in explaining peculiarities in their 

 breeding experiments with other species. 



The Jimson Weed, Datura Stramonium^, is historically of interest 

 to students of heredity, since before the appearance of Mendel's work 



1 A number of species have been established based on forms which differ genetically 

 from D. Stramonium by single factors. Thus D. Tatula is the purple spiny form, 

 D. laevis of Naudin and D. Bertolonii of Godron is the white, smooth-capsuled form. 

 The contrasting pairs of genetic characters so far discovered are spiny and smooth 

 capsules, purple and white flowers associated with purple and green stems, and many and 

 few nodes between the cotyledons and the first fork. We have preferred to include under 

 the name D. Stramonium all the forms which differ by single Mendehzing factors as well 

 as various named biotypes which differ from D. Stramonium at best in minor characters 

 chiefly of leaf and habit. 



Journ. of Gen. xi 2 



