Embryo of Sciadopitys verticillata . 411 
process in the formation of the megaspore tetrads in Sciadopitys I have no 
doubt, for it was repeatedly demonstrated by a large number of prepara¬ 
tions showing every step in the process. 
It was stated above that the presence of starch granules was a charac¬ 
teristic of the megaspore-mother-cell, and that previous to the reduction 
division the starch was rather uniformly distributed throughout the cyto¬ 
plasm. Just before the second division in the formation of the tetrads, 
however, the bulk of the starch grains settle in the base of the mother-cell. 
The result of this is that when the tetrads are formed, the basal cell of the 
axial row contains much more starch than the other cells (Figs. 32, 33, 
34, and 35). This is an interesting point because this basal cell becomes 
the only functional megaspore of the axial row. Fig. 33 represents the 
tetrads of the axial row fully organized, with the basal cell containing an 
abundance of starch, the middle cell with its two free nuclei, and the top 
cell of the row with its single nucleus. Fig. 34 shows the axial row 
where the two free nuclei of the middle cell have shifted their position, 
demonstrating quite conclusively that no cell membrane separates them. 
This figure also shows that the nucleus of the top cell is already betraying 
signs of disorganization. 
The basal megaspore of the axial row now enlarges, but its growth is 
quite slow. Between the stages represented in Figs. 35 and 36 fully four 
weeks have elapsed. But during this period the two nuclei of the middle 
cell and the nucleus of the top cell show every evidence of degeneration, 
and they eventually become quite abortive. The first noticeable change in 
the functional megaspore is its great elongation down through the tapetal 
cells, as shown in Fig. 36. This is now followed by the formation of a large 
central vacuole which causes a growth in all directions. Fig. 37 represents 
a longitudinal section of the functional megaspore and the three abortive 
megaspores as they appear six weeks after the organization of the axial 
row. It will be seen that the functional megaspore now consists essentially 
of a huge vacuole with but a thin film of cytoplasm at the periphery, and 
a single nucleus at the base. A more highly magnified representation of 
the last vestiges of the abortive megaspores is shown in Fig. 37. 
During all of these stages in the development of the megaspores the 
number of tapetal cells has increased considerably, so that eventually there 
are several layers of them surrounding the axial row. 
The outline drawing in Fig. 13 is intended to represent the relative 
position and condition of the two gametophytes in the ovule as they appear 
at the end of the first year’s growth, which closes about the middle of July. 
It will be seen that the pollen-tube has not penetrated beyond the tissue of 
the pollen-cushion, and that the large functional megaspore lies embedded 
in the centre of a large group of nutritive tapetal cells. No further changes 
take place in either gametophyte until the following spring. 
