Chapter IX —149— On Migration 



mist, Dr. Jeffrey (1917, Chap. XVII), in discussing the hypothesis of 

 recapitulation, gives among other examples the following : — 



"In a conifer like the larch, which is diflFerentiated in habit from the mass of the group 

 by its deciduous foliage, we find in the seedling that the leaves persist for several years, 

 thus reveaUng the probable ancestral condition for the genus. An additional example 

 among the dicotyledons is supplied by the oak. The adult in northern oaks is characterized 

 by deciduous leaves. Oak seedlings and saphngs, however, even in the case of typically 

 northern species, retain their leaves during the winter, thus recalling a situation charac- 

 teristic of the Uve oaks of warmer latitudes which have evergreen foliage and represent 

 anatomically the primitive type of organization" (p. 235). 



Species Not Having a Full Cycle of Development: — In some plant 

 communities it is not uncommon to find species that do not pass 

 through a full cycle of development, i.e., they vegetatively develop 

 normally and flower but do not bear fruit, or they lead a purely 

 vegetative type of life bearing neither flowers nor fruits or, lastly, they 

 do not attain even a normal vegetative development. Such species 

 show clearly that their origin is alien to that of the plant community 

 of which they now form a part. For instance, on meadows in the 

 U.S.S.R. such sedges as Carex vesicaria, C. gracilis, etc. vegetatively 

 develop normally but do not flower. The same holds true for the 

 steppe cherry of the U.S.S.R., when growing not on the steppes but a 

 little farther north in the southernmost part of the zone of dense oak 

 woods. Similarly, Caltha palustris, a plant growing ordinarily in 

 swamps or near bodies of water, is found occasionally in meadows, 

 where it does not bear flowers and even vegetatively develops poorly, 

 the fact that it grows here being evidence that these meadows were 

 formerly swamps. Deciduous, Hght-loving plants, herbaceous species 

 that develop normally only under conditions of ample sunlight, are 

 sometimes found in the undergrowth in dense spruce forests, where 

 they cease altogether to flower and even have a poor vegetative de- 

 velopment. 



The fact that in the flora of Spitzbergen there are a considerable 

 number of plants that fail to produce seeds gave grounds for Andersson 

 (1910) to consider that this flora developed under more favorable cli- 

 matic conditions, warmer than those at present prevailing, and, hence, 

 that it does not now have optimum conditions for growth and de- 

 velopment. Vaccinium uliginosum grows in Novaya Zemlya, but it 

 neither flowers nor bears fruit there (Regel, 1935). Rubus arcticus is 

 found in many plant communities in Finland, but either to the north 

 or south of the optimum zone (62°-65° N.), despite normal flower 

 development, it often fails to bear fruit, being propagated vegetatively 

 (Saastamoinen, 1930). The same phenomenon has been observed in 

 the U.S.S.R., where the optimum zone lies between 60° and 64° N. 

 (RozANOVA, 1934). Cernjavski (1937) has reported that Prumis 

 laurocerasiis is found in beech woods north of Vlasina (Jugoslavia), but 

 that it does not bear fruit there. 



Extinction of Species: — If changes in climatic and other habitat 

 conditions actually induce migrations of species, then any plants of 

 such species remaining in the original area are subject to extinction. 

 There are numerous facts confirming this. Paleobotany is replete with 



