44 8 THE GERM-PLASM 



The question as to why this transmission is of such rare 

 occurrence must, however, be considered more closely. I am 

 inclined to seek the causes of this fact in the processes of 

 ' reducing division ' and amphimixis, to which the reserve germ- 

 plasm, but not the ' blastogenic ' germ-plasm, is subjected. Let 

 us suppose that the two were precisely similar at first with 

 respect to their contained modified determinants N^, each pos- 

 sessing a small majority of them : the shoot must then exhibit 

 the variation, but only certain germ-cells would contain a 

 majority of N^ the rest containing a minority of these deter- 

 minants in consequence of the diversity resulting from the 

 reducing division. It is true that two germ-cells containing 

 majorities of N^ might unite in fertilisation ; but this extremely 

 favourable case would only occur very rarely. — when, as assumed, 

 the majority in the reser\e germ-plasm was only a slight one ; 

 while the other cases, in which amphimixis leads to N^ being in 

 the minority, would take place much more frequently. 



It is. however, by no means certain that reserve germ-plasm 

 and ' blastogenic " germ-plasm must contain a similar percentage 

 of N^. The two may very well differ in this respect, and it is 

 extremely probable that a larger percentage of N^ in the reserve 

 germ-plasm leads to the formation of seeds which give rise to 

 seedlings exhibiting variation. We may therefore suppose that 

 in the one case, when the ' blastogenic ' germ-plasm contains 

 even a small majority of X^. the modification of the shoot will 

 actually occur : and that in the alternative case, in which the 

 reserve germ-plasm alone contains a majority of N^ variation 

 will take place in a larger or smaller number of seedlings in the 

 following generations. When both contain a majority of N^ 

 the shoot must vary, and some of the seeds arising irom it 

 must transmit the variation. 



This explanation is not so hypothetical as it might appear. 

 Certain facts point with certaintv to the conclusion that these 

 ' sports ' in many cases really contain only a very slight majority 

 of modified determinants. In most bud-variations reversions 

 to the original form are of frequent occurrence, both in the 

 buds themselves and in the generation derived from them either 

 by seeds or buds. This has alreadv been mentioned in the 

 chapter on reversion, and is so well known that a brief state- 

 ment of a few cases will suffice. In the botanical gardens at 

 Bonn. Professor Strasburger showed me an immense horn- 



