102 



The Journal of Heredity 



hybrids were tnie, it would still be 

 necessary to inquire whether the types 

 of variation found in Oe. lamarckiana, 

 Oe. biennis, Oc. ^randiflora, and other 

 speeies are merely the result of hybrid 

 processes, or whether mutation and 

 hyl)ri(lizali()n are distinct ]3rocesscs.- 



MISSIIAPEIN BUDS 



The petals in the bud of 

 Oenothera lata arccrumpled, 

 causing it to ])e misshapen; 

 the anthers are sterile or 

 nearly so, and relatively 

 few seeds are produced. 

 The buds are stouter and 

 more barrel-shaj)ed in this 

 mutant than in any of the 

 other forms except gigas. 

 These buds are natural 

 size. (Fig. 3.) 



The cell studies of the Oenotheras have 

 aVjundantly ];roven the latter view. 

 The nature of the ex])lanation of muta- 

 tions is also very usefully limited as well 

 as illuminated V)y the cytoloj^'ical results. 

 Mutations of course occur in h\-brids as 

 well as in pure strains, and it is usually 

 possible without much difficulty to ])ick 



out the mutants in hcteroj^eneous F2 

 hybrid families. Confirmation of many 

 such cases can afterward be made by 

 cytolo^^ical study, and others can be 

 analyzed by brecdinj.^ from them. 



As illustrations of the new point of 

 view with rej^ard to mutations we may 

 select three of the mutants of Oenothera. 

 A flowering shoot of Oe. lamarckiana is 

 shown in fig. 1. The mutants, lata, 

 gigas, rubricalyx are all derived from 

 this species, the last, however, being a 

 secondary mutation, which originated 

 directly from nibrinervis, itself a mutant 

 from Oe. lamarckiana. 



oexothi;r.\ l.\t.\. 



In this mtitant and certain others, 

 duplication of a chromosome has taken 

 place, and the writer showed some years 

 ago^ that this happens through one 

 chromosome of a pair passing into the 

 wrong nucleus in the reduction division. 

 It is now known* that lata has con- 

 stantly lv5 chromosomes instead of 14 

 in the nuclei of all its cells. Fig. 2 

 shows a rosette of lata with its deeply 

 crinkled and peculiarly obtuse leaves. 

 This mutant also has a peculiar habit 

 of growth, and its buds are misshapen 

 (fig. 3), the anthers being almost com- 

 pletely sterile. Various other features 

 characterize this very interesting form 

 which was first discovered by Dc \'ries 

 as early as 1887. 



Not only is the extra chromosome 

 constantly associated with these peculi- 

 arities of lata, but its presence deter- 

 mines the inheritance of lata, for its 

 offspring consist chiefly of lata (with 15 

 chromosomes) and lamarckiana (with 

 14 chromosomes) in varying i)ro])ortions. 

 Oe. lata a])i)cars in dillercnt races and 

 species (inckiding Oc. biennis) when 

 this irregular mciotic division occurs. 

 The licculiarities of lata thus arise from 

 the fact that its nuclei contain 15 in- 

 stead of 14 chromosomes. This con- 

 dition arises in the fertilized egg and is 

 passed on to every cell of the plant by 

 the mitotic mechanism. 



' Sec Gates, Hreeding experiments which show that hybridization and mutation are indcpcmlent 

 phenomena. Z<-itschr. f. Abst. u. Vcrerbungslehre 1 1 :' 209-279. Figs. 2.S. 



* A study of reduction in Oenothera ruhrinervis. Bot. Gazette, 46:1-34. Pis. 1-3. 



* See Gates and Thomas. A Cytological study of Oenothera mut. lata and Oe. mut. semilata 

 in nlation to mutation. Quart, journ. Micro. Sci. 59:.S23-571. pis. 35-37, figs. 4. 



