Oct., 1923] 
DARLING — CHROMOSOME BEHAVIOR IN ACER 
451 
material. Bouin’s solution gave the better results in fixation, causing less 
shrinkage of the cytoplasm and less clumping of the chromosomes. The 
best results in staining were obtained by using the safranin, gentian violet, 
and orange G combination. The sections were first bleached for twelve 
hours in full-strength commercial hydrogen peroxide; following this they 
were stained one minute in a saturated, 50-percent alcoholic solution of 
safranin; five minutes in a similar solution of gentian violet; a few seconds 
in an aqueous solution of orange G; the slide was then flooded with absolute 
alcohol followed with clove oil, which was allowed to remain until the stains 
had been extracted so as to give the desired differentiation. This method 
gave a large number of excellent preparations showing marked differentia¬ 
tion between the nucleolus, linin, and chromatin contents of the cell. 
Heidenhain’s iron-alum haematoxylin stain was used as a supplementary 
one, but it did not give the satisfactory differentiation of the triple stain. 
Observations 
Attention was given primarily to the nuclear changes in the pollen 
mother cell during the stages of its first division. The somatic cells of the 
flower stalk and of the roots were examined as well as several megaspore 
mother cells. The pollen mother cells were exceptionally good for study in 
that each flower bud frequently showed several stages of development, a 
single loculus of an anther often including a progressive series of stages from 
one end to the other. 
In the earliest stage to be found in the pollen mother cell, the chromatin- 
staining material exists as several well-defined bodies, varying somewhat 
in size, which are distributed about the periphery of the nucleus; a few of 
these bodies, however, appear to be scattered through the nucleus, and some 
are usually lying against the nucleolus (PI. XXXI, fig. 1). Not infrequently 
two chromatin bodies are found lying near each other; because of the 
similarity in size and position one is led to believe that they belong together 
as a pair. The distance between the individuals of a pair varies; sometimes 
they are nearly in contact, while in other pairs they are separated by a 
space at least equai to their own width. Some of the bodies do not appear 
at first to be paired, yet in view of their subsequent behavior it is not 
difficult to associate practically each one with a nearby mate. It is not 
easy when one sees so many conspicuous cases of pairing in the nuclei of 
this stage to believe that these are merely chance positions, as interpreted by 
Mottier in Acer negundo. The number of these chromatin bodies is probably 
twenty-six, as determined by an examination of numerous complete nuclei. 
The linin occurs as very fine, faintly stained threads, usually forming an 
irregular netlike structure to which the chromatin bodies appear to be 
attached. Occasionally enlarged nodes will be observed on the linin where 
two threads cross or come together; these nodes are distinguished from the 
