Chapter IX —145— On Migration 



relationships of the plants participating in the experiment. For in- 

 stance, Asperula, upon being transferred to greenhouse conditions, no 

 longer had a dormant period and grew without interruption, thus show- 

 ing its relationship to tropical genera of the same family. The genus 

 Leucojum under greenhouse conditions did not enter a dormant period 

 in the fall months but retained its summer dormant period, thus indi- 

 cating its Mediterranean origin. Lastly, Polygonatum retained its 

 normal dormant period corresponding to the cUmatic conditions of 

 Central Europe, testifying to its holarctic origin. 



Consequently, any lack of correspondence between climatic periodi- 

 city and the periodicity of the phasic development of a plant is neces- 

 sarily reflected in some sort of disharmony between the latter and its 

 habitat conditions. This problem has been subjected to detailed in- 

 vestigation by ScHARFETTER (1922). He found that the diversity of 

 periodicity could be classified into two main groups. To the first group 

 belong species the periodicity of whose life cycles corresponds to the 

 periodicity of the Central European climate, so that a plant utilizes all 

 the time suitable for its development. For instance, the apple tree has 

 its dormant period in the winter, flowers in the spring, then develops 

 leaves, and toward autumn begins to fruit. CHmatic and life-cycle 

 periodicity correspond completely. To the second group belong species 

 the periodicity of whose life cycles is in disharmony with the climatic 

 periodicity. As an example we may take Colchicum aulumnale, which 

 flowers late in the fall, when the ovaries formed are most likely to be 

 destroyed by the winter frosts, and the fruits of which ripen only in the 

 spring of the following year, after which this plant, in contrast to most 

 others, enters into a dormant period for the entire summer. Here, in 

 all probability, is reflected the periodicity of the climate of the Medi- 

 terranean Region, characterized by a vegetative period with two breaks, 

 the first in the summer, due to lack of rainfall, and the second in the 

 winter, due to low temperature. 



Hence, the conclusion may be drawn that, if climatic and life-cycle 

 periodicity correspond, the home of any given plant is the country in 

 which it is found and in which its habitat conditions have not under- 

 gone change. If, on the other hand, such correspondence is lacking, the 

 natural conclusion will be that the given plant arose under other cli- 

 matic conditions. Scharfetter considers that in this case the home of 

 the plant should be sought in another place and the plant itself be 

 regarded as an immigrant in the given region. This conclusion, how- 

 ever, is not obligatory, since the indicated disharmony in periodicity 

 might be due to changes in climatic conditions in situ or to changes 

 in the plant itself. 



This retention by some plants of a periodicity out of harmony with 

 the general rhythm of the surrounding vegetation creates a situation 

 such that these plants do not find themselves in competition with the 

 other species in the same plant community. This gives us a clue to 

 the cause of the preservation of these species in places formerly con- 

 stituting part of their potential area but now lying outside it. The 

 fact that there exists such a diversity of periodicity among species 

 belonging to the present-day flora of Europe may easily be explained by 

 the great climatic changes that have time and again occurred on that 

 continent, inducing numerous migrations of its species. 



