120 A CYTOLOGICAL INVESTIGATION OF SOME SPECIES 
gave good results so that the maxim „the older the better” 1) does not 
apply to Iron-haematoxyline solutions in the tropics. 
In a good preparation the chromosomes and nucleoli should be blue- 
black, while all other parts should be unstained. After some trials» a 
large number of preparations were obtained in this condition. 
Besides the haematoxyline-stain, saffranine-staining was given a 
trial, but gave no satisfactory results, possibly because the stain was 
to quickly removed from the chromosomes at the high temperature in 
the laboratory. 
The count of the chromosomes was always done under a homogene 
immersion !/,,t®, num. apert. 1.3 or ander the apochromatic homog. im- 
mers 1.5 mM. num. apert. 1.3 of Zerss, these objectives being combined 
with the compensation-ocular 12. The karyokinetic-figures selected 
for the chromosome-counts have always been drawn as exactly as pos- 
sible by means of the drawing-apparatus of ABBE. Subsequently the 
drawing was carefully compared with the microscopical image and, 
whenever necessary, corrected. 
Figures for reproduction also were drawn by the aid of the ABBE- 
apparatus. With few exceptions the apochromat 1.5 mM combined 
with the compensation-ocular 12 was used for this purpose. The dra- 
wingpaper was then lying on the laboratory-table so that the enlarge- 
ment of the drawing surpassed that of the microscopical image. This 
had the advantage that the shape of the very small chromosomes could 
better be reproduced than in a drawing on a smaller scale. For repro- 
duction the drawings werereducedto 2/4 of the drawn size, the enlarge- 
ment now being practically the same as that of the miscroscopical 
image. Chromosomes visible at a high adjustment are drawn dark, 
while those visible at a lower adjustment are reproduced in a lighter 
shade. | 
À large white screen placed in the sun, outside of the window served 
as the source of light. In Pasoeroean one is pretty sure to have a cloud- 
less sky during all of the morning hours. The screen threw a stron- 
ger light on the mirror of the microscope than gas-glowlight, the heat 
of which moreover was unbearable at the tropical temperature. 
*) T. J. Stomps. Kerndeeling en Synapsis bij Spinacia oleracea L. Dissertatie 
1910, 9.26. 
