W. Hatkson and Ida Sutton '2i):\ 



the suj(j^»8tion injuio l)y Miss PclKw in her disc^usHion of " TyjX'H of 

 Sogn^^itioii'." Tho |m>|)not.y nl' the coiniKirison botwccn the jihs* ►elation 

 of ft chanict'er with ono of tho sexes in the aise of a herinnphriKlit^' plant 

 luui the phenomenon in bisexual animals commonly calle(| sex-linkage 

 may In* (jiiestiontMl. hut until we know more preeis<*ly how s<'X in animals 

 is rolatini t^» the phiMiomena in the flowering plant, no unjustiHabh; 

 Assumption is made an<l no si'rious confusion can hn aiused by their 

 use. If, following om* methrnl of interpretation, we regard poll(;n-mother 

 colls, IkMug the latest diploid stage, as the equivalent of male animals, 

 we can rcivsonabiy speak of thi' character — here doubleness — carried by 

 the j>ollen-gniins, jus linked with maleness, and singleness as linkc^i 

 witli femaleness. The comparison, though not certainly valid is at 

 present defensible. The relation of the hermaphrodite to the dioecious 

 condition, whether in animals or in plants h;is not yet been represented 

 by any factorial scheme which is thoroughly satisfactory. On a survey 

 of the various sexual arrangements followed among plants we meet a 

 difficulty in attempting to choose any fixed moment common to all the 

 cycles, which can serve as a starting point for the institution of homo- 

 logies. The difficulty is intensified when we proceed to the case of 

 animals. One obvious suggestion is that the reduction-division pro- 

 vides such a common fixed point. Though I am not disposed to look 

 upon that event iis the only occasion on which Mendelian segregation is 

 effi^cted, I readily agree that many segregations presumably do happen 

 then, especially that by which sex is usually determined among animals. 

 Such observations however as those of the Marchals and the new evidence 

 discovered by Collins- show almost beyond question that even within 

 the group of Mosses sex-segregation may occur at different moments in 

 the different cycles. 



With equal propriety we may regard the actual gametes as the fixed 

 point common to all and therefore hgniologous in all the cycles, but we 

 have still to face the difficulty that such a critical segregation as that 

 which determines sex (and probably others) may be sometimes effected 

 at the reduction-division, sometimes before it, as at least in monoecious 

 flowering plants, and sometimes after it as in Collins's Funaria. 



The facts practically drive us to the conception that the ordinal 

 |X>sition of the reduction-division can be shifted in the cycle, and that 

 segregations which in some cycles precede reduction are in other cycles 



' Jour. Gen. 1917, vi. p. 310. 



- In the present number of Jour. Gen. 



Journ. of Gen. viii 14 



