Embryo of Sciadopitys verticillata . 41 7 
The division of the body-cell nucleus takes place immediately over the 
neck-cells of an archegonium, and this gives rise to two male nuclei of 
unequal size. Definite male cells are not formed, but merely male nuclei, 
as in the Abietineae. 
The contents of the tip of the pollen-tube are discharged into a single 
archegonium. 
A single megaspore-mother-cell is organized, whose nucleus undergoes 
a heterolytic mitosis, and resulting in the reduction in the number of 
chromosomes. 
The sporophyte has sixteen chromosomes and the gametophytes eight. 
After the reduction division of the megaspore-mother-cell nucleus no 
cell-plate is formed. The two daughter-nuclei lie freely in the cytoplasm. 
The first step in the formation of the megaspore tetrads is the same as that 
of the microspore tetrads. 
The division of the daughter-nuclei occurs simultaneously, but the 
spindles lie one behind the other, and not side by side as in the micro¬ 
sporangium. 
As a result of this second division the axial row of megaspores consists 
of three cells, the middle one of which contains two free nuclei. 
The basal cell of the axial row becomes the functional megaspore, the 
other two become abortive. 
The functional megaspore becomes very large, and contains a huge 
central vacuole, but no further germination takes place until March of the 
following year. 
A distinct tapetum, consisting of two or three layers of large nutritive 
cells, is organized, and completely envelops the germinating megaspore. 
The tapetum is evidently of archesporial origin. 
The megaspore remains unicellular until March of the second season’s 
growth. 
The nucleus now divides, and this is immediately followed by numerous 
free nuclear divisions. 
The resulting free nuclei become distributed in the parietally-placed 
cytoplasm, and the first or primary prothallial cells are formed by the 
development of cell-walls. 
The organization of the permanent prothallial tissue is brought about 
in the manner described for the majority of the Coniferales. 
The archegonia originate at the apex of the prothallium. They are 
four or six in number, and each is enveloped by its own single layer of 
nourishing jacket cells. 
During the fertilization period the inner walls become curiously modi¬ 
fied by heavy, reticulated, chitinous-like thickenings. 
The archegonia are isolated from one another by sterile tissue, and 
each is provided with a deep archegonial chamber. 
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