34 VARIATION. 



factor we have been studying. It does not influence the plants 

 from without, for sugar-maize and starch-com may be grown in 

 the same field in ad j acent rows, and if pains are taken to exclude 

 crossing, the seeds of one row will only give sugar-com-plants, 

 and the seeds in the other row will only produce starch-com. 

 This proves, that here we are dealing with a developmental 

 factor which is transmitted through the germ, which is present 

 in the starch-com, and there helped to produce the transform- 

 ation of sugar into starch, and which is lacking in the germ of 

 sugar-com. It must be a fundamentally different thing, an 

 inherited developmental factor. Its natiure we cannot directly 

 infer, as we cannot isolate it from the plant which carries it. 

 One day it may be possible to find a chemical difference be- 

 tween the germ-cells of a sugar-com, and of a starch-com, but as 

 yet, no such difference has been detected, in spite of the ef- 

 forts of Mr, Levallois. By comparing the two cases, we see that 

 the way in which calcium as a non-inherited developmental 

 factor affects the final result of the individual growing from a 

 germ, and the way in which in the case of our maize-example, 

 an inherited developmental factor affects the final qualities 

 of the individual growing from a germ, is comparable. Both 

 factors help to change the way in which the development pro- 

 ceeds by influencing a certain stage of it. 



The study of the action of the different factors which influ- 

 ence the development of the organisms and so contribute to 

 their final qualities, is very much more difficult for the inher- 

 ited factors than for the environmental factors. For, as it is 

 relatively easy experimentally to regulate the influence which 

 each environmental factor, temperature, salts, pressure, grav- 

 ity, has on the developmental processes, we cannot do the same 

 thing for the inherited factors. As soon as a factor is of vital 

 importance for the life of the organisms to whose development 

 it contributes, we cannot study the way in which the develop- 

 ment would proceed if the factor did not cooperate. And we can 

 therefore only study the action of such factors, if we can regu- 

 late the grade of their action, from optimum down to a mini- 



