MUTATIONS IN THE JIMSON WEED 



Albert F. Blakeslee and B. T. Avery, Jr.^ 

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



IN a recent article in the Journal of 

 Heredity (March, 1917) the writers 

 pointed out the availability of the 

 common Jimson Weed (Datura stra- 

 monium) as an illustration of Mendelian 

 phenomena. Data, in addition to those 

 already published by Bateson and 

 others, were reported showing the regu- 

 larity with which the factors for purple 

 and green stems and for spiney and 

 smooth capsules followed the laws of 

 segregation. The writers have recently 

 determined the presence of another pair 

 of factors affecting the node number 

 and habit of the plant as is shown by 

 the two specimens in Fig. 13. Aside 

 from these three pairs of factors just 

 mentioned and a possible fourth which is 

 under investigation, no other Mendeliz- 

 ing factors, so far as we are aware, have 

 been definitely determined for the Jim- 

 son Weed. During the past few years, 

 however, we have discovered in our cul- 

 tures a number of mutative variants of 

 greater or less distinctness which, so far 

 as studied, seem to be inherited in a 

 manner different from that shown by 

 simple Mendelian characters. We do 

 not wish in this article to go into a de- 

 tailed discussion of the method of their 

 inheritance. Suffice it to say that these 

 mutations are of sudden, though rather 

 rare occurrence and transmit their char- 

 acters — chiefly through the female sex — • 

 to only a part of their offspring. We 

 desire here merely to present a few of 

 the more marked types in order to 

 give some idea of the extent of depar- 

 ture which they show from the normal. 

 The mutations are distinguished from 

 the normal plants from which they arise, 

 not merely by single visible differences. 



but by a complex of characters which 

 seem to be inherited as a whole wehn 

 transmitted to their offspring. Leaf 

 and capsule characters are perhaps the 

 most conspicuously affected, although 

 the growth habits and flowers are also 

 involved in the mutations. The flow- 

 ers, however, fail to show the marked 

 range in color and morphological varia- 

 tion exhibited in many species. The 

 mutations in Datura are distinguished 

 by the same kind of differences appar- 

 ently that characterize mutations in the 

 classical genus Oenothera. 



The capsule is perhaps the best part 

 of the plant to serve as a single example 

 of a given mutation. Its outline differs 

 as seen from different sides. Fig. 5 is a 

 photograph of capsules from a single 

 normal plant arranged to show the in- 

 ternal structure and the resulting out- 

 lines in two positions. All the fruits are 

 correctly oriented in relation to the 

 central cross section. While in this 

 section (d), cut midway between the 

 base and the apex, two cross-walls 

 apparently divide the ovary into four 

 cells; the section at the left (e), cut 

 higher up, shows that only a single sep- 

 tum extends completely to the apex. 

 The capsule is in fact, therefore, two- 

 celled with the placenta forming a false 

 partition running part way to the top. 

 The outline of the surface in consequence 

 appears ovate on the placental side (a) 

 and more nearly cylindrical or ellip- 

 tical on the septum side (b). Typical 

 examples are shown in Fig. 6 from two 

 normal plants and from a number of 

 mutations. At the top are two normals 

 showing the spiney and spineless condi- 

 tion already explained as forming a 



1 Died in France, June 18, 1918, while in service in the Medical Detachment, 30th Infantry. 



Mr. Avery, while scientific a.ssistant to the senior author, personally handled all the mutants 

 discussed in this paper. It is largely due to the keenness of his powers of observation that they 

 were discovered. He is also responsible for finding tlie first "Globe" mutant which started the 

 investigation of variability in the Daturas. 



Ill 



