EVIDENCES OF MUTATION 77 



to loss of something the parent possessed. For this reason 

 he calls them *' retrogressive varieties." 



Two very vigorous mutants the giant {gig as. Figs. 16, 18, 

 22) and the red-veined {ruhrinervis) De Vries considers to have 

 acquired additional characters not present in the parent, and 

 for this reason he regards them as genuine *' elementary 

 species " (having attained a new progressive characteristic). 

 The giant is no taller than its parent species but much 

 stouter, with larger leaves and flowers. Its cells contain 

 twice as many chromosomes as those of the parent species, 

 which fact is considered very important by some cytologists. 

 A wide-leaved mutant {lata. Figs. 20, 25) has one extra chro- 

 mosome in its nucleus (14 + 1 = 15). 



The red-veined mutant {ruhrinervis) has more red on its 

 leaves and stems than has the parent species; its stems are 

 also more brittle, the bast fibres having thinner walls. 



Two other mutants are naturally feeble, not strong enough 

 to survive in a wild state. They are albida (the pale whitish 

 mutant), and ohlonga (having oblong leaves on feeble plants, 

 about half as tall as the parent species). See Figs. 19 and 23. 



" These seven new forms," says De Vries, " which diverge 

 in different ways from the parent type, were absolutely con- 

 stant from seed. Hundreds or thousands of seedlings may 

 have arisen, but they always come true and never revert to 

 the original 0. Lamar ckiana-type.^* Several other mutants 

 have been described by De Vries, among them scintillans, 

 but they are less constant in character than those already 

 mentioned. Their behavior need not here be considered. 



A fact deserving especial attention in connection with De 

 Vries' experiments is the repeated occurrence of the same 

 mutation year after year in pedigree cultures from self -fer- 

 tilized plants, showing that these particular variations occur 

 with some regularity. 



Starting with nine plants transplanted from the field De 

 Vries carried a culture through seven subsequent generations, 

 always planting seed of Lamarckiana parents, with the results 

 shown in Table 6. 



