1915^ Outline on the Theory of Descent 21 



There are some more or less well known practices which 

 incidentally seem to support this hypothesis — for example 

 the growing of bacteria under adverse conditions such as ex- 

 cessive heat with a view to reducing their virulence. Certain 

 disease-producing forms so treated may then be safely in- 

 jected into the human being, whereas before such treatment 

 it would have resulted fatally. Southern market gardeners 

 pretty generally purchase northern grown seed where early 

 crops are desired. The explanation is that short northern 

 growing season somehow speeds up the life processes so that 

 the cycle is complete before cold weather. Seed from plants 

 so grown are supposed to inherit this rapid maturity. 



Tower, a zoologist of Chicago University, in his experi- 

 ments with potato beetles found that species carried from 

 Chicago were so altered by a stay at Tucson, Arizona, under 

 desert conditions that when carried back to Chicago some 

 years later they were unable to withstand the winter. Ac- 

 cording to Tower no selection is practized and this condition 

 is gradually brought about. 



Bordage, a botanist of Reunion, a French island off the 

 coast of Madagascar, reports that European peaches carried 

 to Reunion retain their deciduous habit permanently at 

 higher altitudes, but in the coastal region the leafless period is 

 gradually shortened until after 20 years they are completely 

 evergreen. Seedlings of such trees show the acquired char- 

 acter to the same extent as the parent tree, but no more. 

 Furthermore they retain this character even to the second 

 generation in higher altitudes where trees that have not 

 been so modified shed their leaves every autumn. 



Besides such cases there have been many experiments de- 

 vised primarily to prove this proposition. Bonnier, a mem- 

 ber of the French Academy of Sciences, published in 1895 

 an extensive series of experiments. In all he handled 105 

 species. Plants growing in the lowlands were transplanted 

 to alpine conditions. In a few years these had acquired the 

 aspect of the characteristic alpine species of the same genus 

 even to cell and tissue structure. When carried back to the 



