150 LUTHER BURBANK 



What they are like must for the present re- 

 main only a matter of conjecture. 



But that they are definite mechanical struc- 

 tures of unthinkable smallness, represented by 

 chemical atoms in specific combinations, we can- 

 not doubt. And in revealing to us the size and 

 character of these atoms, the modern physicist 

 gives us aid in supplementing the vision of the 

 microscopist and in helping to make it seem at 

 least a possibility that the definite factors of 

 heredity have a physical basis within the micro- 

 scopic chromosomes. 



The conclusions that give this assurance are 

 based on various almost infinitely delicate tests 

 that are made in the modern physical laboratory. 



Summarizing these in a few words, it appears 

 that the physicist and chemist are now able to 

 make definite computations as to the size of the 

 molecules and atoms that make up the structure 

 of all matter. And the figures they present, 

 when they have taken a census of the atom, are 

 such as to give us full assurance that even so 

 small a structure as the minutest chromosome 

 within the nucleus of a plant cell contains mol- 

 ecules and atoms in such numbers as to make 

 possible an infinite complexity of arrangements 

 and therefore an infinite diversity of resulting 

 qualities. 



