SHOBTEB ARTICLES AND DISCUSSION 



89 



principle, it is probable that his mis- 

 interpretation arose from the asso- 

 •ciation in his mind of my communica- 

 tion with Mr. Cannon's paper on ' A 

 Cytological Basis of Mendel's Law,' 

 where unfortunately the error in ques- 

 tion was not avoided. This paper I 

 first saw after its publication. 



In point of fact the cytological evi- 

 dence on which Sutton based his sug- 

 gestion leaves quite undecided the 

 question whether any definite order is 

 followed in the grouping of the 

 ■chromosome-pairs in the equatorial 

 plate, and places no obstacle in the 

 way of assuming that their position 

 is a matter of chance, i. e , that pa- 

 ternal and maternal chromosomes may 

 lie indifferently toward either pole, 

 and that consequently all combinations 

 of paternal and maternal chromo- 

 somes may be produced in the gametes. 

 To employ Sutton's graphic illustra- 

 tion : if the number of chromosomes be 

 taken as 8 and designated as A, a, 

 B, b, C, e, D, d (large letters denoting 

 paternal chromosomes and small ones 

 the corresponding maternal), the 

 chromosome-pairs in the equatorial 

 plate might, so far as the cytological 

 evidence shows, present any or all 



ABCD abCD aBcD 



the groupings — ; — r- , - ^^;, - . — . 

 "= ^ ^ abed ' A Bed' AbCd' 



and so on, which gives a possibility 

 of 16 difi"erent combinations in the 

 gametes and of 256 in the zygotes or 

 ofi'spring. If the number of chromo- 

 somes be 24 (a very common number ) , 

 the number of possible combinations in 

 the gametes becomes more than 4,000 

 and in the zygotes nearly 17,000,000 

 (Sutton). The assumption is, there- 

 fore, in full harmony with the fact 

 that offspring may show many dif- 

 ferent combinations of characters indi- 

 vidually traceable to four grandparents 

 ■or a greater number of more remote 

 ancestors. 



Despite the immense range of mixed 

 variation and inheritance thus per- 

 mitted under the assumption, a point 

 •of real difficulty, not touched on by 



Mr. Cook, is the relatively small num- 

 ber of chromosomes as compared with 

 that of transmissible characters; for 

 if the chromosome-hypothesis, as de- 

 veloped by Sutton, be valid, it would 

 seem to follow that each chromosome 

 stands not for one, but for many, char- 

 acters, and these should form a co- 

 herent group in inheritance. Coherent 

 groups of associated characters have, 

 however, been recognized by many 

 observers, including Mendel himself; 

 and in this direction definite evidence 

 for or against the chromosome hy- 

 pothesis may perhaps be obtained by 

 the comparative study of variation in 

 nearly related species that diff'er in the 

 number of chromosomes, though this 

 presents a problem of great complexity. 

 Regarding cases of non-conformity to 

 the so-called Mendelian law or prin- 

 ciple, Sutton has endeavored to show 

 that they do not invalidate the sug- 

 gestions given by the cytological work 

 of himself, Montgomery, Cannon and 

 others. They sufficiently indicate, 

 however, that these suggestions do not 

 yet afford a full or positive explana- 

 tion, but only, in my own former 

 phrase, give a ' clue ' which awaits 

 further development and test. It is 

 entirely possible that the clue may 

 prove false, yet even so it may serve to 

 illustrate that ' fertility of false 

 theories' to which Mr. Cook pays his 

 tribute. In the meantime it is to be 

 regretted that a biologist of Mr. Cook's 

 standing should give currency to the 

 statement that 'The notion that 

 heredity, variation and evolution are 

 the functions of special organs or me- 

 chanisms of cells has no ascertained 

 basis of fact' [1. c, p. 222). This 

 ' notion ' may be true or false, but such 

 an utterance will be truly surprising 

 to any one having some degree of ac- 

 quaintance with the literature of em- 

 bryology and cytology. 



Edmund B. Wilson. 

 Columbia University, 

 September 24, 1903. 



