664 Balls.—The Mechanism of Nuclear Division. 
a plate, or even from a granule of motile linin, in which the chromatin was 
embedded. 
My thanks are due to Mr. R. P. Gregory for his critical assistance and 
advice, and to the Khedivial Agricultural Society for the purchase of the 
3 mm. Zeiss apochromatic. 
Reference. 
Cannon, W. A.: Spermatogenesis in Hybrid Cotton. Bull. Torrey Bot. Club, 1900, p. 161. 
The only other paper concerned with cotton cytology. The observa¬ 
tions agree with the writer’s except in three points. 
1. I have not noticed the ‘ filar plasm ’ in the peripheral cytoplasm, nor 
seen any spindle structures proper in this region. 
2 . The chromosomes in the Egyptian plant appear to be twenty in 
number, not twenty-eight. 
3. The formation of chromosomes is not by mechanical condensation 
of loops. Cannon appears to have fallen into exactly the same error which 
I made in the first observations on the reduction divisions; I carefully pre¬ 
pared drawings of the loops of the thread-rings under the impression that 
they were chromosomes which were getting ready to shrink and thicken 
into the usual ‘ U ’ form, and it was not until I tried to follow out this 
shrinking—and also found mature chromosomes side by side with them— 
that I began to look for another explanation for these loops. 
It is of interest to note that he recorded the conspicuous linin struc¬ 
tures, and attributed the formation of part of the spindle to them, although 
without description or reasons. He also comments on the one-sided arrange¬ 
ment of the chromosomes in prophase. 
The irregular divisions which he describes can be found in all cotton- 
plants if very late flowers or very early ones on rattoons are taken ; they are 
not necessarily due to hybrid constitution, and might very well have been 
provoked by the greenhouse culture he employed. 
I might add that this work was in its present stage before I saw 
Cannon’s paper for the first time. 
DESCRIPTION OF PLATE LIV. 
Illustrating Mr. Balls’s article on the Mechanism of Nuclear Division. 
The drawings were made with the Zeiss 3 mm. apochromatic (excepting Figs. 1 and 2) and 
camera lucida, in blue light. 
Fi g s * B 2, 3> 4> ancl 7 are republished from the Year Book of the Khedivial Agricultural 
Society, 1905. 
Fig. 1. Mature microspore mother-cell, not yet passed into synapsis, although the anther wall 
with its aborting tapetum and parietals shows it to be much older than Fig. 2, which is taken from 
