June, 1903 .] Embryology oj Vallisneria spiralis. 44 1 
tiers. Following this, the four basal cells (r) divide by trans- 
verse walls, thus forming an octant ; the next tier (b) divides by 
longitudinal walls, forming a quadrant ; the next tier ( d ) divides 
into two cells by a longitudenal wall, while at the same time there 
is a transverse division in the tier ( e ) below the suspensor cell. 
These divisions, therefore, give rise to a seventeen-celled embryo 
(Fig. 14.) 
The eight cells from the basal tier give rise to the single termi- 
nal cotyledon ; the lateral plumule develops in the next tier while 
the radicle is developed from tiers, d, e, f, etc. (Fig. 16). Fol- 
lowing this seventeen-celled stage the number of transverse 
divisions is continued in the cell below the large suspensor until 
there are about nine or ten original tiers, the embryo being organ- 
ized from the six or seven terminal ones, and the rest serving as 
suspensor cells. The dermatogen begins to be cut off in the cells 
of the incipient cotyledon and continues to develop toward the 
root-tip (Fig. 15). The original tiers of cells begin to divide 
by transverse and longitudinal walls and this also appears first in 
the cotyledon. The development of the embryo follows quite 
closely that of Say it/a ria . It remains orthotropous and when 
nearly mature shows the usual four regions, cotyledon, plumule, 
radicle and root-cap (Fig. 17.) 
SUMMARY. 
1. The archesporial cell is single and hypodermal in origin. 
2. From the archesporial cell, a tapetal cell is cut off, which 
divides into two. 
3. The megasporocyte produces four megaspores ; sometimes 
the dividing walls are oblique. 
4. The pollen grain has three cells before the pollen is shed. 
5. The embryo-sac is normal in development. 
6. There is a large definitive nucleus, by the first division of 
which a lower vesicular nucleus is formed, cut off by a transverse 
wall from the upper nucleus which forms a small amount of 
endosperm tissue. 
7. The embryo develops as in Sagittaria, with terminal coty- 
ledon and lateral plumule, but remains orthotropous. 
BIBLIOGRAPHY. 
1. Campbell, D. H. "A Morphological Study of Naias and Zannicliel- 
lia.” Proc. Cal. Acad, of Sci., III. Bot., 1 : 1-61. 1897. 
2. Campbell, B>. H. “ Studies on the Flower and Embryo of Spargan- 
ium.” Proc. Cal. Acad, of Sci. 1 : 293-328. 1899. 
3. Cook, M. T. “The Development of the Embryo-sac and Embryo of 
Castalia odorata and Nymphaea advena.” Bull. Torr. Bot. Club , 
29 : 211-220. 1902. 
Hall, J. G. “An Embrvological Study of LJnmocharis Emarginata.” 
Bot. Gaz.. 33 : 214-219, 1902. 
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