AND SPECIES HYBRIDS WITHIN THE GENUS SACCHARUM 119 
paraffine in the usual way. Before the pieces of paraffine, containing 
the flowers, had cooled completely in water, but after they had become 
just sufficiently hard to be cut with a knife, they were taken out of the 
water and so trimmed that they could be cut by the microtome. 
This was done, because it was noticed that completely cooled paraf- 
fine frequently possessed internal bursts, because the outer layer only 
had cristallised regularly and minutely. By removing all superfluous 
paraffine before the cooling had completed, this disadvantage was en- 
tirely overcome. 
The paraffine used had a melting point of 75° C. and allowed the cut- 
ting of sections 20 mikron thick at a temperature of about 28° C. in the 
laboratory. 
For the cutting of roottips a paraffine was used, a little harder than 
the former one and consequently allowing the cutting of thinner sec- 
tions; yet this paraffine had a meltingpoint of but 56°C, showing that 
parafinne of different sources can have very different properties. 
The „Rocking-microtome” of the firm C. VAN DER STADT AND Cy. in 
Amsterdam was used all through the work and.gave every satisfaction 
for these small objects. I began by cutting the flowers into sections of 
7—12 mikron thickness, but later on increased the thickness to 18—20 
mikrons as the thin sections cut through the nuclei, the diameter of 
which varies from 12 to 18 mikron also, while whole nuclei are required 
for a reliable count of the chromosomes. The high temperature in the 
laboratory allowed the cutting of such thick sections as a rule. Early in 
the morning however the temperature occasionally was so low that the 
sections did not stick together so that no parafine-ribbons could be 
obtained; in such cases the parafine containing the objects to be cut 
was previously gently heated. Cross- and longitudinal sections were 
made of the flowers. 
Saccharum-roots are rather hard, because, as is usual among Grami- 
naceae, the outer wall of the dermatogen is thickened. As a consequen- 
ce they allow sections of a thickness of 7— 10 mikron only, which suf- 
fised, as metaphases of karyokinesis only were required for my pur- 
pose. 
The stain used was HEIDENHAINS Iron-haematoxyline. Its solution 
could be kept a short time only at the tropical temperature and some- 
times was spoiled very rapidly. It was therefore always used in a rather 
fresh condition and frequently changed. Solutions a week old, already 
