374 PROVISIONAL HYPOTHESIS Chap. XXVII. 



Part II. 



I have now enumerated the chief facts which every one would 

 desire to connect by some intelligible bond. This can be done 

 as it seems to me, if we make the following assumptions; if 

 the first and chief one be not rejected, the others, from beino- 

 supported by various physiological considerations, will not appear 

 very improbable. It is almost universally admitted that cells, 

 or the units of the body, propagate themselves by self-division or 

 proliferation, retaining the same nature, and ultimately becoming 

 converted into the various tissues and substances of the body. 

 But besides this means of increase I assume that cells, before 

 their conversion into completely passive or " formed material," 

 throw off minute granules or atoms, which circulate freely 

 throughout the system, and when supplied with proper nutriment 

 multiply by self-division, subsequently becoming developed into 

 cells like those from which they were derived. These granules 

 for the sake of distinctness may be called cell-gemmules, or, 

 as the cellular theory is not fully established, simply gem- 

 mules. They are supposed to be transmitted from the parents 

 to the offspring, and are generally developed in the genera- 

 tion which immediately succeeds, but are often transmitted 

 in a dormant state during many generations 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 course of growth. Why I use 

 the term union, will be seen when we discuss the direct action 

 of pollen 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 the stages of develop- 



ment. Lastly, I assume that the gemmules in their dormant 

 state have a mutual affinity for each other, leading to their 

 aggregation either into buds or into the sexual elements. Hence? 

 speaking strictly, it is not the reproductive elements, nor the 

 buds, which generate new organisms, but the cells themselves 

 throughout the body. These assumptions constitute the pro- 













