438 



Stout: The Origin of Dwarf Plants 



quite adequately shown in the illustrations on Plates 26 and 27. 

 The characteristics of the two types can be listed as follows: 



Robust form 

 First year of growth, 0.8— i.i m. 

 Second year of growth, 1.75-2 m. 

 No branching from base of shoots. 

 Internodes about 30 in number. 



Leaves ovate, larger ones lobed, pal- 

 mately veined, densely white stel- 

 late-pubescent beneath, glabrous 

 above; leaves all flat. 



Flowers and fruit are typical H. 

 oculiroseus. 



Dwarf form 



0.4-0.75 m. 



1. 25-1. 6 m. 



Large branches from base. 



Internodes about 30 in number, but all 

 proportionally shorter. 



Leaves identical except that the largest 

 are smaller than the average of 

 robust type; many leaves crinkled. 



Flowers and fruit identical with those of 

 robust form; apparently no smaller. 



While typical plants classed as robust and dwarf were very uni- 

 form in the above characteristics, there were a few plants, as noted, 

 described as intermediates or semi-dwarfs, which possessed in some 

 degree of development one or more of the characters of the dwarf 

 form but which in the second year of growth were less distin- 

 guishable. 



The mutant of Oenothera Lamarckiana that most nearly ap- 

 proaches in its characters the dwarf Hibiscus is, of course, Oe. 

 nanella. The principal characteristics of this plant compared 

 with those of the parent form as given by the description of De 

 Vries may be given as follows: 



Robust: 



Oe. Lamarckiana 

 1.5-1.8 m. tall. 



Secondary 

 strong. 



branches abundant and 



Leaves ovate-lanceolate; long petioled, 

 much crumpled surfaces. 



Flowers with petals 3-4 cm. long; buds 



thin, tapering to a point. 

 Fruit and seeds normal. 



Oe. nanella 



Dwarf: about one-fourth as tall as 0. 

 Lamarckiana, often blooming when 

 10-20 cm. tall. 



Secondary branches lacking or nearly 

 absent. 



Internodes much shorter making leaves 

 and flowers more compact. 



Leaves sessile or nearly so; broad at 

 base, often auriculate or heart- 

 shaped; petioles very brittle. 



Flowers very nearly as large; buds 

 often laterally twisted. 



Fruit and seeds of almost normal size. 



The dwarf Oe. nanella differs from Oe. Lamarckiana in nearly 

 all of its vegetative organs. De Vries maintains, however, that 

 such a mutation is brought about by a change iri the activity of 



