123 
Acer negundo , L., and Staphylea trifolia , A. 
delicate threads, while the attenuated parts also appear as connecting 
threads. The result is that the daughter nucleus consists of a number of 
larger and smaller lumps, irregular in shape, and connected by anastomosing 
threads. During the process one or more nucleoli make their appearance 
in each daughter nucleus, at the same time extra-nuclear nucleoli are still 
present in the cytoplasm (Fig. 23). Each daughter nucleus consists, there- 
fore, of a lumpy network, together with one or more nucleoli. The chromatin 
is distributed chiefly along the nuclear membrane (Fig. 24). A more detailed 
description of the formation of the nuclear membrane and the nuclear cavity 
or vacuole will be given below in connexion with Staphylea , which, on 
account of the larger size of the cells, is a more favourable object for the 
study of this phase. 
The second mitosis. Whether the process of reticulation, alveolization, 
or fragmentation of the chromatin described in the foregoing, is carried to 
the finely divided state that is recognized as the resting condition, I am not 
able to state with certainty. This is held to be a matter of little theoretical 
importance, chiefly for the reason that in some plants the chromatin of the 
daughter nuclei reaches the finely divided state of a resting nucleus, 
while in others it does not. The daughter nuclei divide simultaneously, 
the spindles being formed as multipolar complexes which change to 
the bipolar form as has been described for many other plants (Fig. 25). 
In this cell, which is typical, the chromosomes have not as yet been 
brought into the equatorial plate. Each is composed of two lumps, 
and these pairs of lumps are assumed to be the two pieces formed 
by the longitudinal splitting of the somatic chromosomes on their way to 
the poles in the preceding mitosis. In this second mitosis the chromosomes 
are arranged in a regular compact plate at the mature spindle stage. 
During the process of spindle formation nucleoli are present, lying either 
among the spindle fibres or out in the cytoplasm (Fig. 25). The grand- 
daughter nuclei are formed in a manner similar to those of the first mitosis. 
The four nuclei are connected by systems of connecting fibres, before cell- 
division takes place as in many other Dicotyledons (Figs. 26 and 27). All four 
granddaughter nuclei are alike, both as to the nature and amount of 
chromatin and the presence of nucleoli. 
Staphylea trifolia, L. 
In certain important respects, Staphylea is a more favourable object for 
a study of mitotic processes than Acer negundo and other species of Acer 
now under investigation, partly because of the larger size of the cells and 
nuclei, and partly because of the clearness with which other and secondary 
phenomena are brought to view. I have decided to present the details of 
each separately, rather than to combine the corresponding steps under 
common headings. This is done because of the greater ease with which the 
