igis] HUTCHINSON— ABIES BALSAMEA 459 



The fertilization of the nucleus of the ventral canal cell has been 

 seen in several instances. One of the male nuclei fuses with the 

 ventral nucleus (figs. 15, 17, 21); the stalk nucleus also may be in 

 close proximity (figs. 17, 18). Sometimes two tubes enter the 

 archegonium, in which case male nuclei from different gametophytes 

 may fuse with the ventral nucleus and egg nucleus respectively 

 (fig. 21). The chromatin of the fusion nucleus condenses near its 

 center (fig. 18), and the first division takes place. Two successive 

 divisions (figs. 16, 23, 24, 26) result in four nuclei, which as might 

 be expected, are generally arranged in pairs (figs. 22, 25). The 

 nuclei of this ventral proembryo range in diameter from 40 to 50 n; 

 those of the proembryo proper from 60 to 65 ^; otherwise the 

 similarity is very marked (figs. 32, 53, 54). 



Nuclear changes 



The changes in size of the nuclei located in the egg cytoplasm 

 are the most readily measured of all the modifications; moreover, 

 the increase or decrease in volume will serve to indicate the extent 

 of the qualitative changes which occur. Immediately after the 

 division of the central cell the egg nucleus measures about 30 n in 

 diameter (fig. 7). At the time of fusion its length approximates 

 100 m (fig- 19); during the approximation of the chromatin groups 

 160 m is the maximum measurement (fig. 27), and during anaphase 

 of the first division the diameter is again reduced to 50 or 60 fi 

 (fig. 46). The changes in size of the daughter nuclei are less 

 marked; the diameter varies from 20 jx at telophase (fig. 52) to 65 n 

 in the resting stage It is not surprising that the egg nucleus should 

 vary greatly in structure while increasing to 60 times its original 

 volume, and again decreasing to one-tenth its attained volume. 



During the early stages of the first division, and even before 

 the chromatin groups have united, four differentiations of the 

 '"nuclear" material are evident. The chromatin group or groups 

 occupy less than one-tenth of the space within the nuclear mem- 

 brane (figs. 27, 28, 42). The spindle fibers are intranuclear in 

 origin (fig. 28). Large, vacuolate, irregular, deeply staining 

 masses are distributed throughout the whole area. The greater 

 part of the nuclear cavity is pervaded by slender filaments, which 



