Gates: On the Nature of Mutations 



103 



THE GIAJNT PRIMROSE 



Rosette of Oenothera gigas, another mutant from Lamarck's species. 

 The leaves are larger and thicker and with rather blunt tips. 

 With the exception of a few features, this sport breeds en- 

 tirely true. Reduced in size in reproduction. (Fig. 4.) 



The mutation is therefore a nuclear 

 change, which is represented in every 

 cell of the organism, and it will be found 

 that the same is true of every mutation, 

 at least in plants. They are germinal 

 changes of such nature as to be repre- 

 sented in every cell, having been propa- 

 gated by mitosis from the fertilized egg. 



OENOTHERA GIGAS. 



This mutant represents another kind 

 of germinal change — tetraploidy. A 

 rosette of gigas is shown in fig. 4 and 

 full grown plants in fig. 5. The plant is 

 larger and stouter in nearly all its parts, 

 except in height. There are various 

 other modifications from Oe. lamarck- 

 iana, as in the shape of the leaves, and 

 a striking feature is the presence of 

 four-lobed instead of three-lobed pollen 

 grains — a condition not known to occur 



in any other evening primrose. Man}^ 

 of these peculiarities, though perhaps 

 not all, result from the tetraploid con- 

 dition, — the nuclei contain 28 instead of 

 14 chromosomes and as a result the 

 nuclei and cells in all tissues of the 

 plant are conspicuously larger.^ 



The doubling in the chromosome 

 number, however it has taken place, 

 is a distinct process from the irregular 

 chromosome-distribution which gives 

 rise to the lata type of mutation, for in 

 this case the whole chromosome series 

 has been doubled. Tetraploidy is now 

 known in a long list of plant and animal 

 species, which must have originated 

 suddenly from a related species, in the 

 same manner that Oe. gigas appeared. 

 Here again the change is a cell change, 

 propagated by mitosis to every part 

 of the organism. 



* Gates, R. R. The stature and chromosomes of Oenothera gigas De Vries. 

 schung3: 525-552, 1909. 



Arch. f. Zellfor- 



