12 Lawson . — The Gametophytes, Archegonia , Fertilization , 
now increases considerably, and free nuclear division proceeds at a rapid 
rate. The cytoplasm and nuclei, as they increase, accumulate in 
greater abundance at the lower end,, and as this accumulation goes on, 
the large vacuole becomes correspondingly smaller and is confined to 
the upper end of the prothallium. Up to this time the shape of the 
prothallium has been more or less irregular in outline, the upper region 
remaining more or less constricted as compared with the broad middle and 
lower portions, and there has been no trace whatever of any cell-plate 
formation between the free nuclei. A portion of the prothallium in this 
condition is shown in Fig. 14. 
In his recent work on the formation of the endosperm in Sequoia 
sempervirens , Arnoldi (1900) finds that as the parietal layer of cytoplasm 
thickens it accumulates in great abundance at the lower end of the prothal- 
lium. Free cell-formation now proceeds in the lower and upper regions, 
but in the region surrounding the vacuole, structures (‘ Alveolen ’) similar 
to those described by Mile. Sokolowa (1891) in the formation of the 
endosperm of other Conifers are organized. The ‘Alveolen’ ultimately 
give rise to ordinary cellular tissue. He also reports that the archegonia 
are developed only in the tissue derived from the c Alveolen.’ 
My own observations on the thickening of the parietal layer and the 
accumulation of the cytoplasm and nuclei in the lower and upper regions 
agree very closely with those of Arnoldi. I was, however, unable to observe 
the formation of ‘ Alveolen ’ as he describes. As the long narrow vacuole 
continues to decrease in size, the cells surrounding it become larger. And 
these are no doubt the structures Arnoldi interprets as ‘ Alveolen.’ As we 
shall point out later, the archegonial initials are not confined to this region. 
A careful study of this stage in the development of the prothallium 
has convinced me that the final division of all the free nuclei which 
immediately precedes cell-plate formation is nearly simultaneous. In 
a single section over two hundred and fifty mitotic figures were counted. 
Many of these spindles showed the chromosomes at the equator. Some of 
them, even at the lower and the upper regions, showed the daughter-nuclei 
formed with the connective fibrils between them (Fig. 15). The nuclei in the 
vicinity of the vacuole divided in the same way and at the same time as the 
other nuclei, and I therefore could not confirm Arnoldi’s observations on 
the formation of ‘ Alveolen ’ in this region. That this was the final 
division of the free nuclei was shown quite conclusively by the fact that 
cell-plate formation had already begun between some of the daughter- 
nuclei in various regions of the prothallium. 
With so many nuclei undergoing division just about the same time 
they presented every possible phase of mitosis. Some of the nuclei were 
enlarging and just preparing to divide, many showed the chromosomes at the 
equator, others showed the chromosomes on the way to the poles, others again 
