1905] SHATTUCK—ULMUS AMERICANA 219 
3. The pollen grains leave the tetrad stage March 16 to 18 and 
generally show tube and generative nuclei at this time. By March 
23 the male cells appear, while the dehiscence of the sporangium 
occurs from March 25 to 27. 
4. The single megaspore begins to germinate February 15, result- 
ing in eight to sixteen and occasionally more free nuclei. 
5. In many instances the pollen grains thrust tubes through the 
openings in the exine in from two to five directions before coming 
in contact with the stigma, but only the one gaining such contact 
develops. 
6. The pollen tube generally enters through the micropyle, 
though it has been found piercing the nucellus at various places and 
even making its way down the funiculus; it may also branch pro- 
fusely, but this seems to occur only in the cases of belated tubes. 
ne The male cells leave the pollen grain as soon as the tube is 1"™ 
im length, remaining close to its tip, and were always found side by 
side; they appear in their early existence to be fastened together by 
their adjoining ends. 
- The tube nucleus does not leave the pollen grain. 
9. Double fertilization was observed, taking place March 28 to 
31, the first male cell fusing with the endosperm nucleus. 
to. The endosperm nucleus generally divides before the fertilized 
gg, forming large, multinucleolate nuclei. 
_ HU. The embryo is of the massive type, the suspensor cell enlarg- 
Ing but little. 
12. An antipodal egg is not uncommon. 
13. Two embryos are occasionally found in the same sac. 
_14. Two embryo sacs are sometimes formed in a single nucellus 
with an egg apparatus in each. 
_ 15: Chalazogamy was not certainly found, but from indications 
it May occur, 
T am indebted to Professor Joun M. Courter and to Dr. 
HARLES J. CHAMBERLAIN for efficient direction and assistance. 
Wasupurn CoLLEcE, Topeka, KANsas. 
LITERATURE CITED. 
Marcaret, Contribution to the embryology of the Amentiferae. 
- Trans. Linn. Soc. Bot. London 3: 409-424. pls. 67-72- 1894. 
1. Benson, 
