Stout: The Origin of Dwarf Plants 



437 



the progenies of different lines of descent, not including the series 

 started from seed in 1915, is given in the accompanying diagram. 



19 1 4. Series VII. 

 27 dwarf. 

 I robust (?). 

 7 intermediate. 

 ^^ [1914- Series VIII. 

 A 45 dwarf. 

 V. I intermediate. 

 \ r 1914. Series IX. 

 \ J 33 robust. 



I intermediate. 



Parent' 



No. 



< 



./ 



/ 



19 1 2. Series I._ 

 I dwarf ,,^ 

 II robusts 

 3 inter- 

 mediate. 



N 



\ 



\ 



No. 2- 



No. 3- 



O No. 4- 



No. 5- 



1913- Series VI. 



45 dwarf. 

 1913. Series II. 



9 plants, robust. 

 1913. Series III. 

 40 plants, robust. 

 J 1913. Series IV. 

 L 27 plants, robust. 

 3. Series V. 

 plants, robust. 



_ri9i3- 

 I 27 



Discussion 



The dwarf type of Hibiscus oculiroseus constitutes a marked 

 and distinct variation from the usual robust type of the species. 

 It has smaller leaves, many of the leaves are crumpled, the inter- 

 nodes are shorter, and there is an increased development of bran- 

 ches. It is such group-differences as these that constitute the 

 elementary species of De Vries, for, as he states (1901, p. 176): 

 " Elementare Arten unterscheiden sich von ihren nachsten \'er- 

 wandten mehr oder weniger in alien ihren Merkmalen." All the 

 changes, however, are considered to be a result of a change in 

 the condition of a single pangen. 



It is difficult or impossible to describe such a mutation in 

 terms of definite characters that have been gained or lost. The 

 ordinary type of development of the leaves and internodes have 

 been modified mainly in the direction of arrested growth, while 

 the amount of branching has been increased, due chiefly to the 

 development of basal lateral buds that usually remain dormant. 



In comparison with the robust type the characteristics of the 

 typical dwarfs are readily recognized, the general effect being 



