GINKGOALES 211 



FERTILIZATION 



In the cycads, at the time when the pollen tubes discharge their 

 sperms, the archegonial chamber is moist but contains no free liquid. 

 There is no liquid in the archegonial chamber except that discharged 

 from the pollen tubes. This feature has been observed by so many 

 in so many cycads that it can be regarded as a well-established fact. 



In Ginkgo, Hirase^s3 reported free droplets of juice in the arche- 

 gonial chamber, sometimes filling it completely. Personally, I have 

 never been able to make observations upon living material at this 

 stage; but material at the formation of the ventral canal cell, and, 

 later, at the fusion of the egg and sperm nuclei, does not indicate 

 anything different from the well-known cycad condition. It is very 

 desirable that both hving material and sections of well-prepared 

 material at this stage should be investigated. 



The egg and sperm nuclei unite near the center of the egg. Ike- 

 NO^^' observed that in rare cases the wall between the ventral canal 

 cell and the egg breaks down and the ventral canal nucleus fuses 

 with that of the egg, a behavior which has been observed in several 

 of the Coniferales. 



EMBRYOGENY 



After fertiUzation there is a period of simultaneous free nuclear 

 division, as in the female gametophyte. The development, however, 

 is very different, for here the nuclei are evenly distributed through- 

 out the dense protoplasm of the egg; while, in the gametophyte, they 

 are kept in a thin peripheral layer of protoplasm by the large central 

 vacuole. There are usually eight free nuclear divisions, giving rise to 

 256 free nuclei. The number may be somewhat smaller through the 

 failure of one or more of the nuclei to divide (fig. 229), 



Walls are then formed simultaneously throughout the embryo, 

 forming cells of approximately the same size. Very little further 

 division takes place in the micropylar region, but there is a vigorous 

 development at the opposite end, and not much between. Conse- 

 quently, there are three not very well-marked regions. The cells at 

 the micropylar end elongate considerably, those in the middle en- 

 large somewhat, while those at the base, through repeated division, 

 become small and numerous (fig. 230). Although there are three 



