256 BOTANICAL GAZETTE [october 



V 



on coming in contact with the ^gg nucleus presses the side of 

 the latter inward (Jig. 16) , and finally fuses with it. A close 

 series of stages covering the period from the escape of the male 

 nucleus from its sheath to final fusion was not secured. The 

 time from the rupture of the pollen tube to the formation of the 

 fusion nucleus is very short. Ovules taken on June 20, 1901, 

 from a twig bearing perhaps a dozen cones, showed all stages 

 from the formation of ventral nuclei to well developed suspen- 

 sors. Not infrequently a male cell in contact with the tip of an 

 ^%%^ and proembryos of four cells may be found in the same 

 complex. 



THE PROEMBRYO, 



The fusion nucleus is in general below the center of the ej 



and remains in this position until the first division is completed. 

 The dividing nucleus is surrounded by a mass of deeply staining 

 cytoplasm {fig. 18), which as the spindle disappears closes in 

 between the two nuclei and envelops them, as shown infig.ig. 



The spindle, as in the first division of the ^gg in other gymno- 



sperms, is intranuclear. When the two nuclei are in the stages 

 shown in figs, ig-20, the cytoplasm above begins to thin out, 

 showing in many instances a vacuole-like space between the 

 ventral nucleus and the proembryo. This space is never entirely 

 free from cytoplasmic masses. In some preparations, as well 

 as in all later stages, it appears more like a break in the con- 

 tinuity of the cytoplasm than like a vacuole [figs. 22-2j). 



The two nuclei sink to the bottom of the egg, lose their 

 rounded form {fig. 20) , and divide simultaneously {fig 21); 

 while the ventral nucleus has enlarged considerably {figs. 22'-2j) 

 and is quite conspicuous. 



The four nuclei resulting from the second division of the 

 proembryo usually arrange themselves in pairs, as shown in 

 fig, 22, which is reconstructed from serial sections. The third 

 division of the proembryo is also simultaneous {fig. 2j), and 

 gives rise to eight free nuclei, and walls appear shortly after 

 this last division. Among the cycads and in Ginkgo, after ferti- 

 lization, there is a long period of free nuclear division before any 



