1907] LAND—EPHEDRA TRIFURCA 



277 



alone being successful. Nearly all of the largest vacuoles in the egg 

 disappear shortly after fertilization, and the cytoplasm becomes more 

 and more homogeneous as free nuclear division progresses. The pro- 

 embryonal nuclei usually become so dense that they can be seen with 

 difficulty in the cytoplasm. 



Delicate cytoplasmic radiations, similar to those figured in the 

 unfertilized egg, stream out from each nucleus and end in a denser ring 

 of cytoplasm. This delicately radiating cytoplasm becomes more and 



h 



fig- 



produce suspensors. Fig. y shows two or four functioning pro- 

 embryos. The first suggestion of walls, or rather cytoplasmic thick- 

 enings, is shown in f^gs. 6 and 7. The functioning proembryos 

 isolate themselves from the surrounding cytoplasm as follows. Cleav- 

 age cracks appear, starting presumably at the equatorial region of 

 the last spindle, although all trace of a spindle has disappeared before 

 cleavage is apparent. An early stage of incomplete cleavage between 

 sister cells is shown in jig, 8. The cleavage cracks, following the 

 feebly defined wall or cytoplasmic thickening, continue until they 

 meet around the nucleus, carving out a more or less irregular mass 

 of cytoplasm for each nucleus. Three of five completely isolated 

 proembryos are shown in -fig, p, which also shows masses of egg 

 cytoplasm that have not been appropriated by the proembryonal cells. 

 At the time the proembryonal cells have freed themselves completely 

 from the ^gg cytoplasm they lie in a nutritive mass derived from 

 various sources. Shortly after fertilization, the walls of the jacket 

 cells, which always have been extremely tenuous, disappear and in 

 most preparations the jacket-cell cytoplasm becomes mixed with that 

 of the egg {f.g. g). Shortly before the walls disappear the jacket 

 cells become binucleate, the nuclei dividing either mitotically or amito- 

 tically. Occasionally mitotic divisions occur simultaneously in every 

 cell of both layers of the jacket, or every division may be amitotic, 

 or both kinds of division may occur in the same jacket. When the 

 latter occurs, the nuclei at the upper end of the archegonium divide 

 amitotically, and these amitotic divisions can easily be mistaken for 

 fusion. Occasionally the jacket nuclei enlarge, fragment, and their 

 chromatin is scattered through the cytoplasm of the jacket cell and 



