l8o INTRODUCTION TO PLANT GEOGRAPHY [CHAP. 



S. A. Cain writes in his Foundations of Plant Geography : ' Ecological 

 advantages may arise from the competitive ability of the polyploids 

 that allows them to associate favorably with or even to replace their 

 progenitors, or from the capacity of the polyploids to occupy new 

 climatic or edaphic situations, and hence areas in which they are 

 not confronted with competition from their close relatives.' 



Altogether it seems that the phenomenon of polyploidy may have 

 considerable significance in ecological and geographical connections. 

 Thus some of the changes which are apt to accompany polyploidy, 

 such as alterations in plant stature and leaf-size, in the frequency 

 and size of stomata, and in hairiness, may affect transpiration and 

 hence the water economy of the plant. Although some of these 

 characteristics are evidently beneficial to polyploids, others, such as 

 their commonly observed retarded rate of development and lateness 

 of flowering, may militate against their own good, weakening their 

 competitive ability. Various physiological changes have also been 

 observed to be associated with polyploidy, including changed cold- 

 and perhaps drought-resistance which may have great survival and 

 hence phytogeographical significance. The outcome, however, 

 apparently varies with circumstances and wath the particular case 

 under consideration. The same is true of life-form changes, 

 perennials being often polyploid in contrast with their annual 

 relatives. These and other features affect the adaptability and com- 

 petitive power of the plant and hence its ecological amplitude and, 

 consequently, geographical distribution. Moreover, any tendency 

 it may have to dominate is thereby affected, and, where dominance 

 is concerned, so is the habitat and, ultimately, the distribution of 

 other species. In view of the ease with which polyploidy may now 

 be induced in plants by various laboratory practices, it may be that 

 this tendency will become of even greater importance in the future 

 than it is today — for example in the production of larger and better 

 crop plants. On the other hand, it should be recalled that some 

 species which lack the benefit of chromosomal races ' do ' just as 

 well as those with polyploids, showing great ecological and geo- 

 graphical amplitude owing probably to a richness in biotypes or 

 larger genetic entities. 



Further Consideration 



E. V. WuLFF. An Introduction to Historical Plant Geography (Chronica 

 Botanica, Waltham, Mass., pp. xv + 223, 1943) ; for various 

 palaeobotanical and allied aspects. 



