410 Laivson. — The Gametophytes and 
be eight, being just half the sporophyte number, which was easily and much 
more frequently estimated to be sixteen. Fig. 28 represents a transverse 
section of the mother-cell in a plane through the equatorial plate, showing 
the eight heterotype chromosomes as they appear in polar view. The 
daughter chromosomes now pass to the poles in the usual way, as shown 
in Fig. 29, and after being more or less crowded together, where it is 
difficult to identify the individual chromosomes from one another, they 
become very much vacuolated by the accumulation of nuclear sap. The 
membranes of the daughter-nuclei are formed as a result of the nuclear sap 
coming in contact with the cytoplasm in the manner described for Angio- 
sperms (Lawson, ’ 04 ). 
It is a curious fact to note that no cell-plate formation follows this 
division. This is shown in Figs. 29 and 30. The two daughter-nuclei lie 
freely in the cytoplasm of the mother-cell, one at each end. The interest 
of this point is its similarity to what occurs in the microsporangium. It 
will be remembered that in all Gymnosperms no cell-plate is formed imme¬ 
diately after the first division of the microspore-mother-cell in the develop¬ 
ment of the tetrads, and that cell-plates are only formed after the 
simultaneous division of the two daughter-nuclei. This is also true for 
the great majority of the Dicotyledons. The process of tetrad formation 
here found in Sciadopitys clears up much of the doubt that has existed in 
regard to the organization and number of cells concerned in the axial row 
of megaspores among the Coniferales. 
The daughter-nuclei resulting from the heterotype division are no 
sooner organized than preparations for the second division set in. This 
division is simultaneous, and several preparations showed the twin spindles 
lying one behind the other in the mother-cell. In regard to their position, 
these differ from the corresponding spindles in the microsporangium. In 
the latter case the spindles lie side by side, notone behind the other. This 
difference has a direct bearing on the position of the cell-plates which are 
formed after this division. The twin spindles are shown in Fig. 31 with 
the reduced chromosomes at the equator, which indicates how exactly 
simultaneous are the divisions. What follows results in a very curious 
arrangement, for two cell-plates are now laid down midway between the 
newly formed daughter-nuclei. Now, as the two spindles lie one behind the 
other in the mother-cell, with their long axes practically contiguous with 
one another, we have two pairs of daughter-nuclei in a single row and prac¬ 
tically in the same plane. By the formation of the cell-plates the end cell 
of each pair becomes separated from its neighbour. No plate, however, is 
formed between the two middle nuclei, and so it comes about that the axial 
row or tetrads are represented by three cells, the middle one containing 
two free nuclei. This curious arrangement is clearly demonstrated in 
Fig. 32 and the four following figures. That this is the regular and normal 
