612 Validity of the Doctrine of Mutation. 
IV. The theory of selection explains the existence of 
useful characters, but does not explain that of useless or 
actually harmful ones. 1 Whereas the doctrine of muta- 
tion assumes that specific differentiation does not take 
place in any definite direction, that mutations are pro- 
duced independently of their adaptive value, and that they 
may survive, provided that they do not prejudice the 
existence or annul the fertility of the individual, the 
theory of selection cannot account for the origin of sterile 
forms of which, nevertheless, there are many. I have 
already mentioned instances of these in the first part of 
this volume, and will here only add a reference to a most 
remarkable sterile form of oats, recently described and 
figured by NOLL ; 2 to the dates 3 and grapes 4 without pips, 
and to the highly branched and absolutely sterile variety 
of our gardens, called Muscari comosum plninoswii, 
which belongs to a species characterized by a tuft of 
sterile flowers at the tip of the normal spike (Fig. 136). 
Instead of giving a further discussion I shall content 
myself with referring to the curious case of Mimulus 
and Torenia, which BURCK has described, and which this 
theory of selection is most evident!}' insufficient. See WASMANN, 
Biol. Ccntralblatt, Vol. XXI, Nos. 22, 23; also EMERY, Gcdankcn zur 
Descendenz- und Vererbungstheorie, Biol. Centralblatt, 1893, Vol. 
XIII, Nos. 13 and 14, p. 397; further W. WAGNER, V Industrie dcs 
Arandna, Mem. Acad. Imp. St. Petersbourg, Vllth Ser., Vol. XLII, 
No. n, 1894; and N. CHOLODKOVSKY, Die Conifer enlduse, Hor. Soc. 
Ent. Ross., XXXI, p. 43. 
1 For a list of these I refer the reader to DEMOOR, MASSART and 
VAX DER VELDE, L' evolution regressive, Paris, 1897, especially pp. 
286-289. 
2 F. NOLL, Sitsungsber. d. Nicdcrrliein. Ges. f. Naturk., Bonn, 
March 4, 1901. 
3 CH. RIVIERE, Societe nat. d'acclimatation, Paris, La Nature, 
1901, No. 1477, p. 247. The tree in question grows near Hamma in 
Algeria. 
4 H. MULLER-THURGAU has given an exhaustive list of wholly 
or partially sterile varieties of grapes in Experiment Station Record, 
XI, p. 16, 1902. 
