472 



The Origin of Polyploids 



lay the foundation for polyploidy. In both this plant and Rhoeo 

 extreme variations in temperature were more effective than con- 

 stant heat or constant cold. Similar results have been reported 

 in other plants by other writers, and some polyploids have been 



TABLE 25 



Results of Experiments on Eggs of Salamanders Subjected 



TO Refrigeration 



(From Fankhauser in the Quarterly Review of Biology.) 



Temperature: 0° to 4.35° C. 



Duration of treatment: Usually 5 to 24 hours. 



' Three additional haploids were found among the nonviable embryos. 



produced by the temperature treatment of plants during an early 

 division of the embryo. 



Temperature changes have been used to induce polyploidy in 

 animals, but among the vertebrates only the amphibians have 

 been studied. Low temperatures have been particularly success- 

 ful in producing triploids of the newt Triturus viridescens and 

 also of the Japanese newt, T. pyrrhogaster, and act, apparently, 

 by suppressing the second maturation (meiotic) division. The 

 egg of this amphibian is in metaphase of the second maturation 



