294 Non-lsolable Races. 
nial species into an annual one. 1 The careful experiments 
of BRIEM lead to the same conclusion ; for he succeeded 
in wintering the sugar beet after it had borne seed and 
in inducing in this way the same plant to bear seed a 
second and sometimes even a third time. 2 All that was 
necessary to bring this about was that the beet in question 
should continue to increase in thickness 3 and accumulate, 
in its new rings of tissue, the necessary quantity of sugar 
and other food-stuffs. 
It is known that summer wheat can be changed into 
winter wheat 4 by a selective process, and that the con- 
verse process may also take place; also that a perennial 
sort of rye is occasionally raised in Russia besides the 
ordinary annual rye. G Numerous annual species also give 
rise to biennial and perennial forms such as Arabis dcn- 
tota and Delphinium Consolida: 7 and as a general rule 
interferences of various kinds with the normal vital pro- 
cesses of the plant are considered to be the causes of these 
changes. 8 
1 Loc. cit., p. ii. 
2 F. STROHMER, H. BRIEM and A. STIFT, Ucbcr uiehrjahn'ge 
Zuckerruben und dercn Nachzucht, Oesterr.-Ungar. Zeitschr. fiir 
Zuckerindustrie, Pt. 4, 1900, with Plate XV. 
3 For facts relating to this growth in thickness see Die abnonnale 
Entsteliung sccundarer Geivebe in PRINGSH. Jahrb. fiir wissensch. 
Bot, Vol. XXII, 1890, p. 35; and Plate III, Fig. 14. 
4 Numerous illustrations of the question dealt with in the text 
are furnished from agricultural experience by C. FRUWIRTH, Die 
Zuchtung der landwirtschaftlichen Culturpftanzen, 1901, p. 146. 
5 DARWIN, Animals and Plants, I, p. 333. 
A. BATALIN, Das Perenuiren dcs Roggcns. A very important 
paper dealing with these questions is H. C. SCHELLENBERG'S Grau- 
bilndens Getreidevariet'dtcn, Ber. d. Schweiz. bot. Gesellschaft, Part 
X, 1900. 
? THEOD. HOLM, On the Vitality of Some Annual Plants, Amer. 
Journal of Science, Vol. XLII, 1891, p. 304. 
s W. BARTOS, Zeitschrift f. Zuckerindustrie in Bohnicn, Vol. XII, 
1898, p. 456. 
