THE CHROMOSOMES OF OENOTHERA LAMARCKIANA. 511 



Returning to the fourteen- and fifteen-chromosome mutants we 

 are led to distinguish the following groups: 



A. 14-chrcmosome mutants. 



1. Naiiella. 



2. Forms with homogeneous pollen and ovules. 



a. With normal fibres; blandina, decipiens. 



b. With brittle fibres: deserens, tarda, fragilis. 



3. Sesquiplex mutants: simplex, secunda, compacta, elongata, 



favilla, linearis. 



B. 15-chromosome mutants. 



1. Lata group. 



a. Semi-lata. 



b. Sesquiplex mutants: albida, flava, delata. 



c. Subovata, sublinearis. 



2. Scintillans group. 



a. Sesquiplex mutants: oblonga, aurita, auricula, nitens 

 distans. 



b. Diluta, militaris, venusta. 



3. Carta group: candicans. 



4. Pallescens group: lactuca. 



5. Liquida. 



6. Spathulata. 



With the exception of those mentioned under B 2 b, the chromo- 

 somes for all of these types have been counted. The homogeneous 

 mutants of the first section do not arise, as a rule, immediately 

 from the parent species, but through the intermediate of half mutants 

 (de Vries 1919). These are, in the sequence given above: problandina, 

 erythrina, rubrinervis, scindens and simplex. All these have 14 chromo- 

 somes. To this group belongs the rubricalyx of Gates, which is a half 

 mutant with 14 chromosomes. Analogous to decipiens is the latifrons 

 which is a homozygous alethal segregate, derived from rubricalyx by 

 Shull (1921, page 362). 



Of the sesquiplex mutants, enumerated in the first section, Oe. 

 simplex is the original type, the others having sprung directly from 

 it. In the group of Oe. lata the mutants albida and subovata are old 

 forms, whereas flava, delata (p. 480) and sublinearis are new derivati- 

 ves from the main type. From scintillans the forms called militaris and 

 venusta have sprung, but auricula and aurita (p. 462) have originated 

 independently. In their external features, however, they closely re- 

 semble Oe. oblonga. Oe. nitens is so like Oe. scintillans, that it has been 



