SUMMARY AND CONCLUSION 465 



as this again depends on the fluctuating variations of these 

 determinants in the different ids. it will not occur to the same 

 extent in all the ids at the same time ; and thus the remains of 

 these reduced determinants are often preserved in individual 

 ids through countless generations, and may occasionally cause 

 reversion to take place when they have accumulated in conse- 

 quence of the ' reducing division ' and amphimixis. 



Sudden variations of bnds have only been observed in plants 

 which also are, or have been, propagated sexually, and in 

 which the structure of the germ-plasm is therefore just as 

 complex as in species in which sexual reproduction alone 

 occurs. These variations are also due to the effects of dis- 

 similar modifying external influences on the determinants 

 contained in the ' blastogenic ' germ-plasm, which is passed on 

 from cell to cell during the process of growth. It would, how- 

 ever, be impossible to understand why only a single bud out 

 of millions should undergo transformation unless some other 

 cause were also at work. This may be due to occasional 

 irregular nuclear divisions, which would give rise to a similar 

 result to that produced by amphimixis in reproduction by 

 seeds, the m.odified determinants of individual ids occasionally 

 becoming accumulated and then taking effect. 



The power of transmission of • sudden ' variations iti plants^ 

 which is apparently very capricious, may be easily understood 

 in principle. As the modification never occurs in all the ids 

 of the germ-plasm, but only in many of them, and as this 

 majority may be a slight or a considerable one. the trans- 

 mission of the variation will depend on whether the majority 

 is often obtained and even increased, or whether it becomes 

 diminished, or even entirely lost, during the reducing divisions 

 and amphimixis, when the plant is reproduced by seeds. In 

 the case of the first alternative, the " sport ' will be transmitted ; 

 while in that of the second, transmission will only occur rarely 

 or not at all. Even details of the apparently enigmatical 

 phenomena of heredity of known ' sport ' varieties — such as 

 those of the balsamines, weeping ashes, the variegated variety 

 of Ballota nigra, and others — thus receive a very simple 

 explanation. 



The capricious transmission of bud-variations by seeds, 

 which only occurs in the smaller proportion of cases, cannot 

 be explained so easily. It is due to the ' blastogenic ' germ- 



