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Cook: EmsBrYoLoGy OF RHIZOPHORA 275 
the ovary (FIGURE 17). As the embryo approaches maturity, the 
cotyledonary structure sets up a second growth which pushes the 
point of union between the cotyledons and the hypocotyl beyond 
the apex of the ovary. The cotyledons and the hypocotyl then 
_ separate and the hypocotyl drops, carrying with it the plumule ; 
while the ovary, containing the outer integument (sac) and cotyle- 
dons, remains hanging on the tree. 
It is very evident that the cotyledons perform an important 
function in supplying food to the growing hypocotyl. The dis- 
integration of the nucellus and inner integument and the forma- 
tion of the enormous endosperm are all important in the nourish- 
ment of the embryo during the early part of its development. 
This may be readily traced by comparing FIGURES 2, 3, 4, 5, 6, 
12, and 17; first we have the beginning of the nucellus and both 
integuments (FIGURE 2) followed by an increase in size of the ovule 
in which the nucellus is very small (FIGURES 3, 4), then the dis- 
integration of the nucellus to form the embryo-sac (FIGURE 5), the 
enlargement of the ovule and disintegration of the inner integu- 
_ ment (FIGURE 6), a further enlargement in which about one-third 
of the embryo and a considerable part of the endosperm are forced 
out of the embryo-sac (inner integument) and lie in the chamber 
of the ovary (FIGURE 12), and lastly an elongation of the hypocotyl 
and diminution of the endosperm (FIGURE 17). 
SUMMARY 
I. Four ovules, but only one fertilized. 
2. Archesporium probably subepidermal and cutting off two 
tapetal cells. 
3. Megaspores probably four in number. 2 
4. Completion of embryo-sac results in complete disintegra- 
tion of the nucellus. ts 
5. Further growth of embryo-sac results in complete disin- 
tegration of the inner integument and formation of a large amount 
of endosperm. : 
AG. Embryo has easily recognized suspensor and is probably of 
the Capsella type. a 
7. The growth of the embryo may be divided into three 
Periods: (1) first growth of the cotyledons, (2) growth of the 
hy Pocotyl, (3) second growth of cotyledons. 
