100 



MORPHOLOGY OP SPERMATOPHYTES 



as they descend. Upon reaching the base of the oospore the four 

 nuclei arrange themselves in a plane and become ensheathed by 

 fibers derived from the nuclear membrane. Two v?alls are then 

 formed at right angles to each other and to the base of the spore, 

 each nucleus thus being separated from the others, but freely 

 exposed above to the general cytoplasm of the spore. Black- 

 man ^'^ speaks of " each nucleus thus being at the bottom of a 

 kind of shaft that opens above," and the same author thinks that 

 the ensheathing fibers, -which disappear at this time, have some 

 intimate connection with the formation of the walls. In any 



event, the appearance of these 

 first incomplete walls is quite 

 apart from nuclear division, 

 and the incomplete segmenta- 

 tion of the cytoplasm presents 

 a peculiarity which is paral- 

 leled in the yolked eggs of 

 certain animals. In fact, the 

 method of receiving food sup- 

 ply into the egg, the organ- 

 ization of a small group of 

 cells to develop the embryo, 

 the setting aside of the great 

 mass of the oospore as a nutri- 

 tive supply, and the appear- 

 ance of the peculiar walls 

 about the basal nuclei seg- 

 menting more or less the cyto- 

 plasmic mass but not cutting 

 it off, are facts which are all more suggestive of the embryogeny 

 of certain animals than of other plants. Chamberlain observed 

 one case in which the first and second segmentations of the 

 fusion nucleus were accompanied by walls, a four-celled group 

 thus appearing near the center of the oospore. 



According to our' observation, the walls which separate the 

 four primitive nuclei, as mentioned above, do not appear until 

 after the nuclei are in an advanced stage of division (Fig. 76, C). 

 The spindles formed by the four basal nuclei are extremely 

 broad and multipolar, but the later spindles are definitely bipolar. 

 The basal nuclei divide simultaneously in a plane transverse 



Fig. n. — Pinus Zarido, the first division 

 of the nucleus of the oospore ; the 

 entire mitotic figure is intranuclear; 

 X 500. — After Chambeklain. 



