26 
J Bretland Farmer. 
to be double from the first. In this respect Professor Lawson’s 
observations are in precise accord with our own (Farmer and Digby, 
On the Somatic and Heterotype Mitoses in Galtonia candicans, 
Bi it. Ass. Rep., Sheffield, 1910). That is to say, each chromosome 
arises with a structural arrangement already in existence identical 
with that which finds its expression in the longitudinal fission during 
the ordinary somatic mitosis. It is this duplex character which has 
been interpreted by Gregoire and his pupils to represent the lateral 
approximation of pairs of somatic chromosomes to form the hetero¬ 
type bivalents, owing to the failure to recognise it at these earlier 
stages. It appears clear, however, that the explanation advanced 
by Gregoire cannot be fitted to the case of Smilacina, any more than 
it could to Galtonia. Each duplicate filament of Smilacina, repre¬ 
sents one longitudinally split somatic chromosome, for they are 
present in the full pre-meiotic or diploid (2x) number. There 
appears to he no room for mistake, inasmuch as they are described 
and figured as entirely separate from one another, furthermore they 
are apparently free from lateral or other anastomoses which in 
Galtonia and other plants so often serve to mask or obscure the 
real course of events. Later on, at a stage corresponding with the 
“ second contraction ” of some authors, the split pre-meiotic chromo¬ 
somes join in pairs, conjugating laterally to form the heterotype 
bivalent (x) chromosomes. The longitudinal fission in each (pre- 
meiotic) chromosome persists more or less obviously until the 
metaphase of the next (homotype) mitosis, when it becomes finally 
effective and brings about the separation of the daughter chromo¬ 
somes at this stage. 
There is, of course, nothing very new in all this, but it furnishes 
a welcome and important confirmation of that interpretation placed 
on the critical stages of meiosis which is becoming more widely 
adopted at the present time. 
It is about ten years ago since several investigators, ourselves 
among the number, working independently of each other, put forward 
these views. They were set forth in some detail in a paper pub¬ 
lished in 1905 (Farmer and Moore) to which Professor Lawson 
makes frequent reference. With the increase of knowledge, ampli¬ 
fication and corrections in detail have naturally been made, but the 
main results then reached have been, in essentials, confirmed by 
further research on the part of my co-workers and myself, as well 
as by others. Different material varies greatly, both as regards the 
clearness with the process can be followed, and the certainty with 
which the evidence can be sifted, and it is to this circumstance that 
the divergence of views which still exists is to be largely attributed. 
In this connection the investigations on hybrid and mutating plants 
have proved of especial value. Thus Gates has observed important 
stages in his studies on CEnothera (subsequently confirmed by other 
students of the cytology of this genus) which appear to be irrecon¬ 
cilable with the very different explanation first advanced by 
Gregoire and his pupils. 
It is unnecessary for me to enter at greater length into the 
controversy which has been going on for a number of years con¬ 
cerning the time at which meiotic pairing of the chromosomes to 
form the bivalents occurs. Nor is it necessary to discuss the 
radically different interpretations which have been placed on the 
