Organs and Fertilization in Picea excelsa. 363 
in the substance of the egg-nucleus ; but the walls of both 
nuclei are still intact (Figs. 49 - 51 ). Later stages in the con- 
jugation of the sexual nuclei have not been observed. The 
fate of the second sperm-nucleus, tube-nucleus, and stalk-cell 
after their entrance into the egg has not been followed in the 
present studies. 
Division of the Fertilized Nucleus and Formation 
of the Proembryo. 
The fertilized nucleus soon divides into two smaller nuclei. 
The karyokinetic spindle of this division is shown in Fig. 53 . 
The two daughter-nuclei thus formed increase rapidly in size, 
and then divide simultaneously. The four free nuclei soon 
increase in size. When they have reached their full size, they 
begin to move down toward the base of the egg (Figs. 53 , 54 ). 
Upon reaching the base of the egg, the four nuclei arrange 
themselves in a plane, and they are surrounded by a deeply 
staining mass of protoplasm, which is much more finely 
granular in structure compared with that of the rest of the 
egg (Fig. 55). 
The four nuclei then divide simultaneously in a plane trans- 
verse to the long axis of the egg (Fig. 56 ). After the complete 
formation of eight daughter-nuclei walls are formed between 
them, and a tier of four completely walled cells is cut off below, 
the upper four nuclei still being freely exposed above to 
the partially segmented cytoplasm of the egg (Fig. 57 )* 
Strasburger (’8 4$) figures the formation of the complete wall 
in the four-celled stage in Picea excelsa , and the figure is 
repeated in his later publications (’97, ’0.2). Blackman (’98) 
also describes, in Pinus sylvestris , the formation of walls 
between the four nuclei. According to him, ‘ the two walls 
are formed at right angles to one another and to the base 
of the oosphere ; each nucleus thus lies at the bottom of 
a kind of shaft which is open above.’ Miss Ferguson (’00 #) 
failed to find any sign of wall-formation in the four- nuclei 
stage, and mentions that ‘ in the five species of Pines which 
B b % 
