EwAKT — Variatmi : Germinal and Environmental. 371 



representing remote as well as intermediate stages in the ancestral history. 

 Judging by the results, one of tlie immediate ancestors may control the develop- 

 ment, or the control may be about equally divided between immediate, inter- 

 mediate, and remote ancestors, the issue, as in many battles, being decided by 

 the quality, individuality, or character (what we call the prepotency) of the 

 successful groups of vital units, rather than by their numbers. 



The combined results of germinal and environinental variation. 



As variation is intimately associated with intercrossing, the best way to 

 illustrate the combined results of germinal variation and the variation in the 

 germ-plasm due to food, temperature, &c., i.e. environmental variation, will 

 be to give the results of a number of intercrossing and interbreeding 

 experiments. 



It may be said that intercrossing only differs from ordinary cross-fertilization, 

 in that the results appear in larger type, are, as it were, magnified. This is true 

 of intercrossing between closely allied races, but not of intercrossing between 

 distinct varieties, and still less between different species. In the latter there is, 

 to use the same simile, a difference in the character as well as in the size of the 

 letters, in most cases a reversion to simpler and more primseval forms. When for 

 several generations, the ancestors have been intimately related and almost identical 

 in chai'acters, the offspring, as a rule, resemble the parents, doubtless, because the 

 vital units or groups of units proceeding from both parents have all very similar 

 tendencies. 



Whether, when the parents have been living under very different conditions, 

 and dift'erin age, vigour, &c., variability (environmental variation) shows itself in 

 the offspring, has not yet been systematically investigated. 



The following are some of the more striking results of intercrossing: — 

 1. The offspring may, down to the remotest details, be all but intermediate 

 between tlie two parents. Examples of this intermediate condition, though 

 not very common, certainly occur. In a cross between black and white birds, 

 black and white feathers may alternate with each other, over a considerable part, 

 if not over the whole body. This once happened in a cross-bred pigeon, and the 

 same thing happens in plants, in e.g. a cross between two species of the tobacco 

 plant, Nicotiana rustica and N. paniculata.* 



In such cases it may be presumed that equally nourished, equally matured, and 

 equally prepotent germ-cells meet and blend in such a way that both parents are 



* Kollreutter, " Vorlaufige Nachricht von einigen das Geschlecht der Pflanzen betreffenden Versuchen 

 und Beobachtungen," 1716. 



3 F 2 



