50 Heredity. 



sist of a, multitude of germs tlirown off from each sepa- 

 rate atom of the organism." 



From the extract we see that the hypothesis is an 

 attempt to show that all the phenomena of generation 

 and development, including those of variation as well as 

 those of heredity, depend upon the fact that each struc- 

 tural unit of the hody is the direct offspring of a similar 

 unit in the body of a parent or of a more remote ances- 

 tor. The cells of the body of one of the higher organ- 

 isms are not only morphologically but actually indepen- 

 dent individuals, reproducing themselves directly in tlie 

 next generation: and the germ of such an organism is in 

 reality an aggregate of these cell-germs. 



Stated more at length, the hypothesis is as follows : 



^' T assume that cells, before their conversion into 

 'form material,' throw off minute granules or atoms, 

 which circulate freely throughout the system, and when 

 supplied with proper nutriment, multiply by self-divi- 

 sion, subsequently becoming developed into cells like 

 those from which they were derived. These granules, 

 for the sake of distinctness, may be called 

 gemmules. They are supposed to be transmitted from 

 the parent to the offspring, and are generally developed 

 in the generation which immediately succeeds, but are 

 often transmitted in a dormant state during many gen- 

 erations and are then developed. Their development is 

 supposed to depend on their union with other partially 

 developed cells or gemmules, which precede them in the 

 regular order of growth. Why I use the term union will 

 be seen when w^e discuss the direct action of j)ollcn on 

 the tissues of the mother plant. 



'' Gemmules are supposed to be thrown off by every cell 

 or unit not only during the adult state but during all 

 stages of development. Lastly I assume that gemmules 



