240 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1936 



the Metazoa. But between the formation of relatively complex 

 bodies such as we find in the vorticellids, or in Volvox, and the still 

 more complex bodies of the Metazoa ending with the vertebrates, 

 there are only differences of degree, not of kind. 



A leaf cut from a begonia plant and laid flat on damp earth will pro- 

 duce new plants, which, in the course of time, will put forth flowers 

 and seed; whence comes the "germ-plasm" of these seeds? Who 

 can doubt that it was distilled from the normal process of metabolism, 

 and is endowed with the power of reproducing new plants. These, 

 in due course, give rise to flowers, and seeds, differing in no wise from 

 plants derived from a "zygote." The protoplasm of this begonia leaf, 

 in short, possessed all the qualities of its race, and in due course 

 built up a new j)lant exactly like that from which it was derived. It 

 could do no other. For though by no known process of analysis 

 could we distinguish between the "germ-plasm" of a begonia and that 

 of a bean, yet each has its own peculiar qualities and endowments, 

 and inevitably they reproduce after the manner of their kind. But 

 they are not immutable. Like all other living bodies, the tissues of 

 which they are made up are all responsive to intensive stimuli, so that 

 ihey of necessity are subjected to a higher rate of waste through such 

 stimuli, and in consequence will absorb more of the "food material" 

 manufactured to sustain life. Hence such parts come, in succeeding 

 generations, to change their shape, and at the expense of some other 

 tissues, which may become reduced to a vestigial condition. As a 

 result new "varieties" and new "species" and genera and so on arise. 

 Throughout the whole vegetable and animal kingdoms these 

 subtle agencies are at work, resulting, as I have said, in "self- 

 regulating" bodies. 



In short, that same "somato-plasm" which builds up the complex 

 human body, bone and muscle and nerve, the oviducts, the uterus, 

 the testes, and sperm ducts, can, and does also build up the ova and 

 the spermatozoa. What we call "heredity" is but the expression of 

 one of the orderly sequences of growth, inherent in the substance 

 which has worked out its own salvation in the course of the ages. 

 That this substance differs in its qualities, in every living thing, is 

 manifested in the infinite variety which living bodies, whether of 

 plants or animals, present. 



The Mendelians account for the results obtained, for example, by 

 crossing tall and dwarf races of peas or fowls with different forms 

 of combs, by attributing these several characters to the agency of 

 "entities", which they designate "genes", or "factors." These, it is 

 held, can be transmitted respectively by the sperm and the ova, which 

 form, at fusion, the "zygote." Tall and dwarf individuals of this 

 hybrid parentage reappear in the second generation. In some cases 



