294 Non-lsolablc Races. 



nial species into an annual one.^ 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.- All that was 

 necessary to bring this about was that the beet in question 

 should continue to increase in thickness"* and accumulate, 

 in its new rings of tissue, the necessary quantity of sugar 

 and other food-stuffs. 



Tt is known that summer wheat can be changed into 

 winter wheat"* 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.^ Numerous annual species also give 

 rise to biennial and perennial forms such as Arabis dcn- 

 fata and Dclpliiniuin ConsoVida-? and as a general rule 

 interferences of various kinds with the normal vital pro- 

 cesses of the plant are considered tu be the causes of these 

 changes.'^ 



"^ Loc. cif., p. II. 



" F. Strohmer, H. BRIE^[ and A. Stift. Uchcr mehrj'dhrige 

 Zuckerriiben und deren Naclicurhf, Oesterr.-Ungar. Zeitschr. fiir 

 Ziickerindiistrie, Pt. 4, 1900, with Plate XV. 



" For facts relating to this growth in thickness see Die ahnonnale 

 Entstchnng sccunddrey Gczvcbc in Pringsh. Jahrb. fiir wissensch. 

 Bot., Vol. XXII, 1890, p. 35; and Plate III, Fig. 14. 



* Numerous illustrations of the question dealt with in the text 

 are furnished from agricultural experience by C. Fruwirth. Die 

 Ziielitting der laudzvirtschaftlichen Culturpflanzen, 1901, p. 146. 



^Darwin, Animals and Plants, I. p. 33:^. 



*^ A. Batalin, Das Perenniren des Roggens. A ver^^ important 

 paper dealing with these questions is H. C. Schellenberc/s Grau- 

 hiindcns Getreidcvarietdten, Ber. d. Schweiz. bot. Gesellschaft, Part 

 X, 1900. 



"Theod. TTolm. On the Vitality of Some Annual Plants^ Amer. 

 Journal of Science, Vol. XLII. 1891, p. 304. 



*'W. Bartos, Zeitsclirift f. Zuckerindustrie in Bolimen, Vol. XII, 

 1898, p. 456. 



