in the Pollen- Mother -Cells of Larix. 289 
out-of-doors. Of several fixations tried, the best results were 
obtained with Flemming’s stronger solution. The sections, 
five microns in thickness, were stained with the triple stain. 
I have also had the privilege of examining some similarly- 
fixed and stained preparations made by Professor R. A. Harper 
and by Mr. H. G. Timberlake. Several of my drawings are 
from Professor Harper’s preparations, and one is from one 
of Mr. Timberlake’s. Living pollen-mother-cells have also 
been examined and compared with killed material. 
The process of spindle-formation may be considered as 
divided into five periods or stages ; the division is somewhat 
arbitrary, and consecutive stages are in no case sharply 
separated from one another. 
1. The Pre-Radial Stages. 
The earliest material that I have studied was gathered and 
fixed October 24. The pollen-mother-cells are still packed 
closely together, but are beginning to round up and separate 
from each other. Each cell seems to be bounded only by 
a distinct blue-staining plasma-membrane ; at least, I have 
been unable to distinguish, by the use of the orange stain, any 
layer of cell-wall material. Between the separating cells is 
a blue-staining material, possibly the old disorganizing cell- 
wall, sometimes appearing as a distinct layer of some thickness, 
sometimes as a cloudy mass. Fig. i, PI. XIV, shows a pollen- 
mother-cell in this stage. Groups of red-staining bodies, the 
chromatin tetrads, are seen in the nucleus, just within, or often 
in contact with, the nuclear membrane ; segmentation of the 
spirem thread, therefore, has already occurred. There is 
usually a single nucleole (sometimes two), * in general of 
a rounded and somewhat irregular shape. Much of the 
irregularity of outline, however, is due to adhering clumps of 
a usually less dense and blue-staining substance — the linin. 
Linin is also found in contact with the chromosomes, and, in 
the form of ragged, wavy, granular fibres, connecting the 
chromatin groups with each other, with the nucleole, or running 
from nucleole or chromosomes to the nuclear membrane. 
