282 General Botany 



U . S. Oepl. oj Agriculture 



Fig. 180. Tobacco plants of the same variety grown from large, medium, and small seeds, 

 showing the relation between the size of the seed and the size and vigor of the seedling. Is 

 the difference in size in the plants due to environment or to differences in the plants them- 

 selves? 



but an occasional branch has three leaves at a node, and another 

 has only one leaf at each node. Variations of this kind are not 

 heritable. Perhaps they are mere accidents of development. 



Heritable variations. These variations are the result of he- 

 reditary differences in the nature of the plant. For example, 

 dwarf nasturtiums were variations that occurred among the com- 

 mon tall forms. The tall nasturtiums showed fluctuations in 

 height, but all the fluctuations were near a certain size. The 

 dwarfs were very different in size at the start, and when bred 

 among themselves it was found that the small size is heritable. 

 Similar variations have resulted in the production of dwarf peas 

 from tall peas, bush beans from the pole beans, bush squashes 

 from squashes with long, trailing stems. The differences between 

 variants are not always so great as in the examples just mentioned. 

 Indeed, the amount of variation may be very small. The several 

 varieties of hma beans, for example, show only sHght differences 

 in shape and size. The varieties of mock orange show small 

 differences in the form of the flower and leaf. The important 

 point about these variations is that the particular characteristics 



