ON VARIETIES IN PLANTS 315 



varieties of this group in that its rachis is strong enough to support the 

 fully developed frond. 



As Benedict has shown the bud mutations occurring in these ferns 

 are more commonly regressive (showing more resemblance to bostonien- 

 sis than to their parent forms), but progressive mutations are found 

 from time to time. These progressive changes take place along three 

 main lines, viz., increase in leaf division (see Fig. 131), increase in ruffling 

 or crisping, and dwarfing (see Fig. 132) ; and any form which has not 



FIG. 132. A series of fronds illustrating progressive variation in ruffling and dwarfing. 

 1, AT. exaltata; 2, var. bostoniensis; 3, Harrisi (or RooseneUi) ; 4, Wm. K. Harris (or new sport 

 of Roosevetii) ; 5, Teddy Jr.; 6-8, dwarf sports of Teddy Jr.; 7, Randolphi. (Courtesy 

 Brooklyn Botanic Garden.) 



reached the limits of possibility in variation along the first and last 

 mentioned lines, may be expected to give rise to new forms showing 

 further progressive variation in one or both of them. 



That these new varieties are produced by mutations in specific factors 

 is indicated by the independence of character changes in series of suc- 

 cessively produced forms that differ in several characters; for example, 

 the appearance of dwarf uni-pinnate forms as sports of dwarf multi- 

 pinnate forms. Various series derived from bostoniensis show progressive 

 degrees of reduction in size of frond. When a dwarf tri- or quadri- 

 pinnate plant throws a uni-pinnate sport the latter retains the dwarf size 

 of its parent. Again the difference between Piersoni and superbissima, 

 its sport, consists of the deeper color and twisted, irregular shape of 

 the latter. When it in turn produced viridissima the new uni-pinnate 



