E. V. Wulff — 146 — Historical Plant Geography 



Disharmony between the Biological Peculiarities of Some Species 

 and Their Present-Day Habitat Conditions: — In many floras in different 

 regions of the globe, particularly in Europe, there may be found a con- 

 siderable number of species, the biological peculiarities of which 

 are not in harmony with their habitat conditions. This disharmony 

 constitutes yet another proof of the fact that climatic changes have 

 taken place that have caused migrations of floras, occasional repre- 

 sentatives of which have remained on the territory of the original area 

 without having become adapted to their new habitat conditions. In 

 most cases such plants will eventually be crowded out by those species 

 which, as regards their biological peculiarities, find themselves in com- 

 plete harmony with their habitat conditions. 



As a characteristic example of such a plant we shall take the genus 

 Cyclamen, which comprises 20 species, distributed primarily in the 

 Mediterranean Basin, particularly its eastern part. This genus is un- 

 doubtedly of ancient, Tertiary origin, this being confirmed by its 

 marked isolation from other genera. Everywhere it grows it has pre- 

 served with remarkable constancy all its biological peculiarities, which 

 fully harmonize with Mediterranean conditions but which, for many 

 of its species, are not at all in accord with their present habitat con- 

 ditions. Most Cyclatnen species flower late in the autumn, when winter 

 is nearly at hand, and in spring or early summer, when the surrounding 

 vegetation is at the apogee of growth, these species lose their foliage 

 and remain dormant for several months, until autumn is well under 

 way, when they enter again into a period of development. Such a life 

 cycle is fully comprehensible under conditions in the Mediterranean 

 Basin with its hot, dry summers and warm, rainy autumns, enabling 

 the vegetation that has become dry and dusty during the summer 

 months to revive and cover itself with fresh leaves and flowers. But 

 under conditions in central Europe, with its rainy summers and cold 

 winters, such periodicity in the life cycle of a plant is not at all in 

 accord with the climatic periodicity. This summer dormant period is 

 not so marked in Cyclamen europaeum, which does not shed its foliage 

 and flowers in the summer. In general, however, this periodicity has 

 been preserved even under conditions of cultivation; it has been over- 

 come by age-long cultivation only in the case of C. persicum. 



As another example of disharmony between the periodicity in the 

 life cycle of a plant and climatic conditions, we may take the ivy 

 {Hedera Helix), whose distribution parallels approximately that of the 

 beech. It flowers in September, in northern regions occasionally be- 

 ginning in August, and in some places continues in bloom as late as 

 January, i.e., during the very coldest months of the year, its fruits 

 ripening, for the most part, only towards spring. Consequently, in 

 nature, flowering of the ivy is rarely observed and then only in warm, 

 protected places; under cultivation, however, it occurs with consider- 

 ably greater frequency. The ivy is, undoubtedly, an ancient Tertiary 

 plant, which became established in Europe in the Miocene stage, when 

 the winters did not cause such a marked break in its development. 

 Although it has become adapted to cold weather, having penetrated in 

 post-glacial times even into Scandinavia, it has preserved the same pe- 

 riodicity as regards its flowering, a periodicity in complete disharmony 



