SELECTION IN PLANT BREEDING 193 



for they knew that many times they had noticed and isolated plants 

 showing new characters from their cultures, and had carefully made 

 selections for further improvement of the new strain, but that genera- 

 tion after generation showed no further progress. LeCouteur, whom de 

 Vries cites as the first known user of the pedigree culture method, had 

 a case in point. From the heterogeneous lot of wheat plants which he 

 was growing, he isolated a uniform type of great merit which he called 

 " Bellevue de Talavera." For years after, this strain was subjected to 

 selection in order to bring about further improvement, but the efforts 

 were made in vain, for no new heritable variations were produced. Yet 

 something was lacking from this theory. Sometimes there did appear 

 to be a gradual improvement by selection. De Vries said that this was 

 merely a temporary improvement made by selection of quantitative 

 variations. He believed that when selection ceased, sooner or later 

 the improved types would return to the original type of the variety 

 from which it had been produced. The real interpretation of the facts 

 and one which fitted all the parts of the puzzle together, came from the 

 work of Johannsen and later investigators. It is an explanation that 

 should have been thought of before, but like many other important dis- 

 coveries, it was too simple for ordinary minds to grasp. Weismann had 

 shown years before that the inheritance of characters acquired through 

 outside influences during the development of the body was probably 

 mythical. His investigations led him to believe that there is a continu- 

 ity between the reproductive or germ cells of different generations, and 

 that the body is nothing but a temporary house built to shelter them. 

 Injuries to the house have no effect on the future generations unless the 

 germ cells themselves are affected. Later Boveri and others, through 

 their cytological studies, showed that the future germ cells are laid down 

 at a very early stage in certain animal organisms and that very few cell 

 divisions take place before the maturation of the reproductive organs 

 and the production of active germ cells. The body cells he found to be 

 built up by continuous cell division of a very different part of the orig- 

 inal fertilized egg. Since no biologist, however, had found or is likely to 

 find similar cytological phenomena in plants, no one seemed to grasp 

 the idea that here was the key to the question that had been puzzling 

 the plant breeders. Johannsen, however, brought matters straight by 

 his experiments on beans. He found that commercial varieties of 

 beans, though pure in grosser characters, such as color, were actually 

 very mixed types when such characters as length or weight were studied. 

 Several investigations were undertaken on size characters, the char- 

 acters most rapidly affected by changes in environment. He found that 

 his commercial variety fluctuated around an average size and that when 

 seeds larger or smaller than this type were selected they responded to 

 it in whichever direction the selection was made. The progeny of the 



