48 THE FLOWERING PROCESS 



seem quite logical, perhaps even obvious, that the winter wheat must 

 have been promoted in its flowering by the low temperatures of 

 winter. Indeed, it did seem apparent to a number of people at least 

 as early as the 1830's, and mention of the phenomenon can be found 

 even before that. In 1849 the New American Farm Book described 

 methods of treating moist winter wheat seed with cold so that plants 

 will head rapidly when they are planted in the spring, and an anony- 

 mous report in 1837 also describes the process. J. H. Klippart 

 described such methods in a report to the Ohio State Board of 

 Agriculture in 1858. Other findings with various rosette-forming 

 biennials as well as cereals appeared sporadically in 1875, 1881, 1898, 

 1899, 1903, 1906, and 1909, for example. 



Some of these reports were made public by Georg Klebs, who 

 spent the years before his rather early death at 61 (1918) at the 

 University of Heidelberg. Klebs probably did more relating to the 

 effects of environment upon plant growth and development than 

 anyone else before Garner and Allard. He had a clear insight into 

 the "specific structure" of the cell, which we would now call the 

 genetic material and identify with deoxyribonucleic acid (DNA), 

 and which he knew was in control of plant growth. He knew that 

 the environment must act upon the internal conditions of the cell and 

 thus influence the manifestation of the "specific structure" without 

 changing the "specific structure" itself. 



Klebs had studied flowering extensively. He had observed that 

 sugar beets and many other biennials would remain vegetative for 

 years when they were kept in a warm greenhouse (unless they were 

 exposed for a time to near freezing temperatures), and also that some 

 plants kept under incandescent lights during the night would flower 

 while controls in the dark remained vegetative. Thus he had the 

 basic information to formulate our present concepts of vernalization 

 and photoperiodism. He was, however, a strong proponent of the 

 nutrition theory, and when the vernalization response was clearly 

 stated in 1910 and again in 1918 by G. Gassner, Klebs discussed the 

 results on the basis of nutrition (see section on theory below), and 

 his results with light were also explained in a nutritional context by 

 considering the extra time for photosynthesis. 



Thus it was Gassner who first introduced the concept of a cold 

 requirement for flowering and attempted an analysis of the phenome- 

 non, although his explanations were somewhat incomplete because 



