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eka eames > Sg eae 

1901 | OVULE AND EMBRYO OF POTAMOGETON 345 
In two or three cases a very large nucleus was found near 
the antipodal end of the embryo sac, the embryo being in the 
stage just described. Its origin could not be determined, but it 
seems reasonable to consider it a derivative of the primary 
endosperm nucleus, and possibly the lower nucleus of the first 
division, as in Sagittaria+ and Potamogeton paucifiorus.$ 
THE. UNIVERSITY oF CHICAGO. 
EXPLANATION OF PLATES II AND III. 
Fig. 1. Micropylar end of nucellus, showing the archesporial cell. 
Fic. 2. Primary sporogenous and tapetal cells. 
Fig. 3. The same at a later stage; nucleus with radiating strands of pro- 
_ toplasm, and surrounded by a hyaline a 
Fig. 4. Tip of a young nucellus; inner i: duteeeinnont and primordium of 
outer integument; sporogenous cell with nucleus in early synapsis stage; 
chromatin massed, dense (deeply erythophilous); nucleolus non-granular 
(deeply cyanophilous) ; two-layered tapetum. 
Fig. 5. Primary sporogenous cell; nucleus in synapsis; a two-layered 
tapetum with an anticlinal wall recently formed. 
Fic. 6. Same with two-layered tapetum; nucleus in synapsis. 
Fic. 7. Same with three-layered tapetum. 
Fig. 8, Same with spindle and cell-plate; epidermis with double layer 
but taking no part in tapetal structure. ; 
Fic. 9. Same with two spindles; upper one nearly transverse; beginning 
of axial row. 
Fig. . Axial row showing two potential megaspores, and the upper 
daughter ne with a spindle. 
Fig. 11, Functioning megaspore more advanced, but no sign of further 
division in either middle or upper cells. 
FIG. 12. Functioning megaspore resorbing the potential megaspores. 
Fig. 13. Embryo sac after the first division; daughter nuclei widely 
separated, with large vacuole between them; six-layered tapetum 
1G. 14. Embryo sac, after second division; remnants of the spindle 
between the nuclei at antipodal end of sac; eight-layered tapetum not all 
shown. 
Fig. 15. Micropylar end of embryo sac, showing cells of the egg-appa- 
ratus; from section adjacent to fg. 16. 
*SCHAFFNER, JOHN H.: Contribution to the life history of Segi#taria variabilis. 
Bor. Gaz. 23 : 252-273. pls. 20-26. 1897. 
5 WIEGAND, Karu M.: Bor. Gaz. 25: 117. 1898. 
