i42 O'NEAL: EMBRYO SAC DEVELOPMENT IN OENOTHERA 
Many of the orders in which the plants with four-nucleate 
embryo sacs are found have also species in which the antipodals 
are ephemeral. It is not clear how the latter condition could 
have given rise to the former. In the Myrtales, as well as in 
other orders in which the tetra-nucleate embryo sac has been 
reported, sacs with sixteen nuclei have been found. If there is 
a genetical relationship between these three conditions, it must 
be looked for in smaller groups. Ishikawa (17) says that the 
tetra-and sixteen-nucleate embryo sacs are to be regarded as rep- 
resenting a derived type, “probably caused by mutation and 
variation in certain stages of phylogenetic development.” At 
the present stage of our knowledge this is probably as accurate 
a statement of the condition as it is possible for us to make. 
Fertilization —The ripe pollen grain as described by Geerts 
(15) for Oe. Lamarckiana has a generative cell and a tube cell. 
The division of the generative cell to form the sperms was not 
observed but it evidently occurs in the pollen tube. Sections 
were found showing the sperms and the tube nucleus in the 
tube. In most cases they are obscured by the large amount of 
starch present in the tube. Ina pollen tube, the tip of which had 
just reached the embryo sac, the sperms and vegetative nucleus 
were observed in the part of the tube in the micropyle. Ishikawa 
(17) found that three sperms were formed in Qe. pycnocarpa 
and Oe. nutans. There are but two developed in Oe. rubrinervis. 
The sperms seem to enter the egg apparatus through a synergid 
as described by Ishikawa, but the material at hand does not 
show enough cases to be positively confirmatory on this point. 
The flowers from which the material for this paper were taken 
were guarded and at the proper time hand pollinated. It was 
found that with midsummer temperatures the pollen tubes 
were able to reach the embryo sac in about thirty-six hours 
after pollination and that fertilization (FIGs. 21, 22) occurred 
soon afterwards. In practice large masses of pollen were placed 
upon the stigmas. The large number of pollen tubes developed 
disrupted the inner tissue of the style to such a degree that the 
extent of their course could be made out by examining the styles 
with a binocular. But comparatively few of the tubes reached 
the micropyles. Numerous theories have been given for such 
failures. One mentioned by Compton (1) and based upon the 
supposed analogy between fertilization and infection in animals 
