The Nature of the Double Spireme in Allium Cepa„ 
BY 
T. REED, A.R.C.Sc., 
Senior Demonstrator in Biology at Guy's Hospital Medical School ( University of London), 
London , S.E. 
With Plates XVIII and XIX. 
ALLIUM CEP A has repeatedly been the subject of cytological investi- 
jljl gation, but there are several phases in its nuclear history which cannot 
be regarded as being clearly understood. 
In the present investigation attention has been more particularly 
focused on the following points : the development and significance of the 
longitudinal fission in the spireme ribbon, the method of origin and grouping 
of the chromosomes in the prophases, and the origin and subsequent fate of 
the nucleoli. 
In view of the recent investigations of Dr. Lawson (10, 11, 12) on the 
significance of nuclear osmosis as a factor in mitosis, the behaviour of the 
nuclear vacuole and its contents during the prophases has also been carefully 
studied. 
Methods. 
Root apices have been almost exclusively used in the investigation. 
These were removed from plants which were grown in culture solutions or 
in soil. The bulbs used for the production of the roots were Sutton’s 
s Reading ’ and ‘ Ailsa Craig ’. 
The fixatives employed were Flemming’s strong and weak solutions, 
either full strength or diluted with an equal volume of water, Hermann’s 
fluid, and Farmer’s acetic alcohol. Various strengths of chrom-acetic acid 
solutions were used, but were not found to be satisfactory. 
In staining, Breinl’s combination was extensively used and gave the 
best results, but Flemming’s triple stain and Heidenhain’s haematoxylin 
were also employed. 
The sections were cut i ju -14 ^ in thickness. 
Prophases. 
During the nuclear * resting ’ stages the bulk of the chromatin is stored 
in the nucleoli ; the remainder of the nucleus contains a fine faintly staining 
reticulum. Where these threads of the reticulum cross one another a slightly 
[Annals of Botany, Vol. XXVIII. No. CX. April, 1914.] 
