The progress of Genetics siuce the rediscovery of Menders papers. 409 



plete inabilitj' to grow^j, we can scarcely avoid the conclusion that 

 in the somatic cell-divisions similar processes wmy be concerned. That 

 segregation precisely similar to that which occurs among gametes 

 may take place in somatic divisions is indeed proved by the existence 

 of bud-sports. The appearance of a glabrous Nectarine on a Peach 

 tree or of a white flower on a red-flowered plant is unquestionably 

 due to segregation, and it is interesting to observe that the characters 

 which segregate in these "sports" are often those which we know to 

 segregate in gametogenesis. Such facts raise the fundamental question 

 whether in the normal process of somatic differentiation, segregations 

 of a similar nature may not occur (see 5, p. 22). This is a field to 

 which the attention of Cytologists might be applied with good pro- 

 spect of results. 



The relation of Mendelian segregation to specific distinctions. 



The time is not fully ripe for a proper discussion of this im- 

 portant question. All that can be yet done is to point out some of 

 the more obvious considerations which the new knowledge suggests. 

 Mendelian segregation proves the unity of characters. Specific differ- 

 ences we must suppose, are built up of characters. Is it a sound 

 deduction that specific differences come into existence by the addition 

 or elimination of such character-units? Now it is scarcely necessary to 

 insist that plenty of the characters which are now known to segregate 

 would be far more than sufficient to constitute specific differences in 

 the eyes of most systematists, were the plants or animals in question 

 brought home by collectors. We ma}^ even be certain that numbers 

 of excellent species universally recognized by entomologists or orni- 

 thologists, for example, would if subjected to breeding tests be im- 

 mediately proved to be analytical varieties. But this is not enough. 

 We must eventually go further; and. supposing such tests to be 

 applicable on a comprehensive scale to great numbers of natural 

 forms, we must ask whether the result of such an investigation will 

 show first that certain kinds of differences segregate and that certain 

 other kinds do not segregate; and secondly whether we shall then 

 recognize that it is to the non-segregating that the conception of 

 species attaches with the greater propriety. For my own part, until 



^) For a striking- example see the case of a hvhrid raised by Messrs. Veitch, 

 between a hybrid Azalea and a hybrid Khododendron. After 16 years careful culti- 

 vation this plant was only 3 inches high and had never flowered (Gard. Chron. 1899, 

 (2) pp. 57 and 95, fig. 41). 



