126 Mottier . — Mitosis in the Pollen Mot her' -cells of 
prevails. The different forms of bivalents observed in Staphylea are the 
same as those described for Acer negundo , with the exception that they are 
much larger and more numerous. Fig. 35 represents a median section of 
a nucleus, while tangential views of nuclei of the same loculus are represented 
in Figs. 36 and 37. In Fig. 36 the long piece of chromatin seems to 
indicate delayed segmentation. Such phenomena are frequent at this stage. 
a , and c, Fig. 38, represent three sections that include the entire nucleus. 
The different sizes and shapes of the bivalents and the presence of the 
large homogeneous nucleolus are typical. In a two bivalents were pushed 
out of the nucleus in sectioning. Nothing is more striking at this stage, in 
this as well as in all other plants studied by the writer, than the perceptible 
differences in the size of the chromosomes, and if such differences have any 
significance in plants, there is, at the present state of our knowledge, no 
means of knowing. Since the various forms of the bivalents are the same 
as those of A. negundo , further details in this respect seem unnecessary. 
Effort was made to ascertain accurately the number of chromosomes, 
but, because of the larger number and of their crowding together at the 
stages favourable for counting, I was unable to convince myself that 
the exact number was determined beyond question. In my judgement the 
haploid number is about thirty-six, or three times the haploid number of 
Acer negundo. Thirty-six was also the number ascertained for Acer rubrum. 
In either case it does not seem probable that the number exceeds forty or 
forty- two. Correlated with this larger number in Staphylea and in other 
species of Acer, is the much larger size of the pollen mother-cells than in 
Acer negundo with its twelve or fourteen bivalents. 
When the chromosomes are distributed in the nuclear cavity following 
their formation, they may be connected with each other, with the nuclear 
membrane, and with the nucleolus, by very delicate threads (Fig. 35). In 
more densely stained cells these threads are distinct, but if the staining be 
less dense they appear faintly or not at all. 
From spindle to telophase. The chromosomes now undergo a con- 
densation until they are arranged in the equator of the spindle, when they 
have attained their minimum size (Fig. 39). The process of spindle develop- 
ment is similar to that in other pollen mother-cells. As described for the 
Lilies and other Dicotyledons, the kinoplasmic fibres may sometimes appear 
first as a weft running parallel with the nuclear membrane, and at a distance 
midway between the latter and the cell-wall (Fig. 35). The fully developed 
spindle is usually sharply pointed at the poles and the various fibres have 
the usual well-known arrangement. A polar view of this stage shows that 
the bivalents are arranged in the form of a circular disc (Fig. 40). They 
are usually more closely crowded together than in this figure. By looking 
at Fig. 40 it might seem that the task of counting is an easy one, and that 
accurate results may be obtained without difficulty, but such is by no 
