June, 1903.] Embryology oj Vallisneria spiralis. 44 1 



tiers. Following this, the four basal cells (c) divide by trans- 

 verse walls, thus forming an octant ; the next tier (d) divides b}" 

 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 tovs-ard the 

 root-tip ( Fig. 15). The original tiers of cells begin to divide 

 by transverse and longitudinal w^alls and this also appears first in 

 the cotyledon. The development of the embryo follow^s quite 

 closely that of Sagiftaria. 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, wdiich 

 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 Saoiffaria , with terminal cot)"- 

 ledon and lateral plumule, but remains orthotropous. 



BIBLIOGRAPHY. 



1. Campbell, D. H. "A Morphological Study of Naias and Zannichel- 



lia." Proc. Cal. Acad, of Sci., III. Bot'., 1 : 1-61. 1S97. 



2. Campbell, D. H. " Studies on the Flower and Enibn-o of Spargan- 



ium." Proc. Cal. Acad, of Sci. 1 : 293-328. 1899. 



3. Cook, M. T. "The Development of the Embn-o-sac and Embryo of 



Castalia odorata and Nymphaea advena." Bull. Torr. Bot. Clnl).,. 

 29 : 211-220. 1902. 



4. Hall, J. G. "An Embryological Study of L,imnochari.s Emarginata." 



Bot. Gaz.. 33 : 214-219, 1902. 



