1904] MERRIMAN: VEGETATIVE CELL DIVISION 179 
gentian violet and orange G, followed by clove oil as a clearing 
agent, gave the best results in differentiating the nucleoli. 
CELL DIFFERENTIATION, 
The transition of meristem cells into permanent tissue is to 
be noted not only in the changes taking place in the nuclei, but 
also in the cytoplasm. As the cells develop into permanent 
tissue, large vacuoles appear in the cytoplasm, and the nuclei 
retreat into positions next to the walls, becoming then elliptical. 
Among the foremost of the problems suggested by watching the 
cells of the meristem pass out from their embryonic condition 
was that of the part played by the chromatin and nucleoli in 
this transformation of an embryonic cell into a tissue element. 
A median longitudinal section reveals the large central cells 
and elongating cells which constitute the plerome. These large 
cells have correspondingly large nuclei and vacuoles in the cyto- 
plasm and a relatively smaller amount of chromatin (jigs. 50, STY. 
In the differentiation of these cells the chromatic substance first 
diminishes, and with this diminution it gradually loses the power 
of forming the karyokinetic figures. The great increase of the 
nucleoli follows from the quantitative reduction of the chromatin, 
while the energy that would have produced new cells becomes 
diverted into the expansion of the nucleus and cell body. The 
central cells reach a maximum of enlargement and then enter 
upon slow disorganization. 
The cells of the plerome elongating to form procambium are 
early conspicuous, being marked off from the large central cells 
of the plerome on the one side and the periblem cells on the 
other by their narrow dimensions and elongating nuclei (figs. 
51-56). Anexamination of these cells when in the act of divid- 
ing shows that the same general changes take place as in the 
meristem cells. The spireme stage is to be frequently seen, as 
well as the separation of the chromosomes. No cell, however, 
was seen which showed the chromosomes drawn into an equato- 
rial plate. Their passage to the poles seems to follow directly 
upon the breaking of the spireme (fig. 5 5): 
The changes leading to the formation of the elongated cells 
must be sought in the meristem cells from which these are 
