300 



SCIENCE 



[N. S. Vol. XLII. No. 1079 



processes influences that make no impress 

 on the morphological structure of the egg. 



The case of the influence of X-rays on 

 fertilizin, already referred to, provides 

 another instance where the effects are with- 

 out direct morphological representation. 

 Doubtless others occur. These eases must 

 of course be accounted for by any explana- 

 tion of the effect of radiation on living 

 organisms. 



The facts, as they are at present known 

 in regard to the effects of radioactivity on 

 living matter, show that life processes are 

 subject to marked changes under the influ- 

 ence of the radiation, a slight exposure be- 

 ing accelerative in most cases, while a more 

 intense treatment is inhibitive or destruc- 

 tive. As a causal factor in these effects, the 

 demonstrable injury to the chromatin of the 

 cells is undoubtedly important; but there 

 are also good evidences that the modifiabil- 

 ity of enzymes under the action of the rays 

 likewise plays a considerable part either 

 directly or indirectly in the resulting in- 

 jury. 



A. Richards 



Woods Hole 



ABE RECESSIVE CHAEACTEBS DUE TO 

 LOSS? 



SmCE the presence-absence theory came into 

 vogue it has become quite customary to re- 

 gard recessive characters as due to the absence 

 of something in the germ plasm on which the 

 corresponding dominant character depends. 

 The nomenclature of the presence-absence 

 theory has been adopted by most writers on 

 Mendelian inheritance, and it has afforded a 

 useful and convenient method of expressing 

 gametic formulas, although, as Morgan has 

 shown, there are cases in which it leads to in- 

 consistent results. While it is often recog- 

 nized that this nomenclature is a purely sym- 

 bolic scheme of indicating how certain char- 

 acters behave in inheritance, the habitual em- 

 ployment of the system in the search for form- 

 ulas which wiU designate by a series of large 



and small letters the gametic constitution of 

 the organisms one is dealing with, has a strong 

 tendency to influence one's views in regard to 

 several important problems of heredity and 

 evolution. I can not but think that the opin- 

 ions of many students of genetics have been 

 unduly influenced by their formulas. Form- 

 ulas are excellent servants but bad masters. 

 Almost involuntarily a certain interpretation 

 is attached to their symbolism which is apt to 

 have the practical effect of actual belief if it 

 does not succeed in producing it. 



Since the establishment of Mendel's law and 

 its successful employment in elucidating many 

 previously enigmatical phenomena of inherit- 

 ance, heritable variations have commonly 

 come to be considered as due to the addition or 

 subtraction of discrete units of germ plasm, 

 the bearers of unit characters. Professor 

 Bateson in his " Problems of Genetics " says 

 in regard to substantive variations that 



we are beginning to know in what such variations 

 consist. These changes must occur either by the 

 addition or loss of factors. 



And further on he makes the following sig- 

 nificant statement : 



Eecognition of the distinction between dominant 

 and recessive characters has, it must be conceded, 

 created a very serious obstacle in the way of any 

 rational and concrete theory of evolution. While 

 variations of all kinds could be regarded as mani- 

 festations of some mysterious instability of organ- 

 isms this difficulty did not occur to the minds of 

 evolutionists. To moat of those who have taken 

 part in genetic analysis it has become a permanent 

 and continual obsession. With regard to the origin 

 of recessive variations, there is, as we have seen, 

 no special difficulty. They are negative and are 

 due to absences, but as soon as it is understood that 

 dominants are caused by an addition we are com- 

 pletely at a loss to account for their origin, for we 

 can not surmise any source from which they have 

 been derived. 



In his more recent address before the Brit- 

 ish Association, Bateson not only interprets 

 all recessive characters as due to loss, but sug- 

 gests that dominant characters may have 

 arisen by the removal of inhibiting factors, 

 thereby causing a " release " of the characters 

 which previously lay latent in the germ plasm, 



