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XXV.—A Study in Chromosome Reduction. By A. Anstruther Lawson, Ph.D., 
D.Se., F.L.S.; Lecturer in Botany, University of Glasgow. (With Three 
Plates. ) 
(MS. received July 11, 1912. Read May 13, 1912. Issued separately November 18, 1912.) 
INTRODUCTION. 
Although the amount of active research that has been carried on during the past 
few years on the question of chromosome reduction and relative problems has been 
very great, the nuclear activities here concerned are still far from being under- 
| stood. We are not yet in a position to draw general conclusions in regard to meiotic 
phenomena. It therefore seems to me desirable that all observations of fact and 
rational interpretations should be placed on record, so that when it becomes possible to 
| generalise, all lines of evidence may be available. 
A careful reading of the literature on meiosis will show that the most divergent 
views and widest difference of opinion expressed are those concerning three distinct 
phases of meiotic activity, viz. :— 
ist, The phase of the nucleus known as synapsis. 
2nd, The formation of the achromatic figure. 
3rd, The act of reduction—especially as to the manner and place of its occurrence. 
It has frequently occurred to me, that if we could concentrate research on these three 
important phases of meiosis many of the difficulties might be removed, and this would 
| lead to a clearer understanding of the problem asa whole. The present investigation is 
therefore not intended as an exhaustive study of chromosome reduction. It is merely 
| an attempt to call attention to certain physiological aspects of the cell during meiosis. 
Tt is believed, for instance, that osmosis and the high state of nutrition that prevails 
are important factors in so-called “synapsis,” spindle formation, and chromosome 
| reduction. 
The material that has been used in the present investigation is Smlacina, the 
advantages of which have already been described in my former paper (Lawson, 19114) 
_|on the phase of the nucleus known as synapsis. This material has been supplemented, 
especially for the reduction stage, by Kniphofia and Aloe, plants which offered excellent 
|material for nuclear study. 
Tur Harty PropHase oF THE First Metotic Division. 
In fig. 1 we have represented a section of a mature microspore mother cell with the 
nucleus in the characteristic so-called reticulum stage. It will be seen that the cell 
TRANS. ROY. SOC. EDIN., VOL. XLVIII., PART III, (NO, 25). 88 
