Recent Work on the Reduction Division in Plants. 11 
colleagues have confined themselves to the description of events 
from the resting nucleus up to the formation of the definitive 
chromosomes. At this point the story is taken up by Professor 
Gregoire in his most recent paper, which deals both with animals 
and plants. By means of a critical investigation of the literature 
and many new observations he has traced the course of events 
with great clearness from the formation of the definitive chromo¬ 
somes to the production of the spore tetrads. In plants the 
definitive chromosomes consist, as Strasburger says, of two 
limbs, and these are, according to Gregoire, parallel, crossed or 
interlaced, and present the form of a V, X, or Y. In certain plants 
the definitive chromosomes have been described as consisting at 
o 
this point of four limbs instead of two, but Gregoire has shewn 
convincingly that at least in some of the examples usually quoted 
this is due to errors of observation. Gregoire uses the word 
“ metaphase ” for the period between the moment when the 
chromosomes first range themselves in the equatorial plane of the 
spindle, and the moment when the chromosomes destined for the 
two daughter nuclei lose contact with one another on their way to 
the poles. Nearly all botanists take the view that when the 
definitive chromosomes range themselves to form the equatorial 
plate at the beginning of the metaphase, they do not lie in the 
equatorial plane, but in a plane at right angles to this, so that one 
limb is orientated towards each pole, and in this position they 
become attached to the spindle fibres. This is called “insertion in 
superposition.” The spindle fibres attach themselves to different 
points of the limbs of the chromosomes, so that these take the 
form of rods if the insertion is terminal, V’s if it is median, and 
hooks if it is intermediate. On their way towards the poles during 
the “anaphase” (the period from the moment when the chromo¬ 
somes destined for the two daughter-nuclei become quite free from 
one another, until the daughter-nuclei are completely formed) each 
of the limbs of the definitive chromosomes undergoes longitudinal 
fission. Each of the daughter chromosomes so formed will be one 
of the chromosomes for the four spore nuclei. The daughter nuclei 
do not pass into a state of complete rest, but their chromosomes 
undergo a varying degree of vacuolarisation and softening of out¬ 
line which sometimes make them difficult to distinguish. In the 
second division (the so-called “homotype”) there is no real fission 
of the chromosomes, since this has already taken place in the 
anaphase of the first division (the so-called “heterotype.”) 
We now pass on to consider how the description of the 
