162 



ARCHEGONIATES. 



the first division of the fusion nucleus in Ginkgo biloba (Fig. 67, A, 

 B, C, D). These processes agree closely with those in Cycas. In 

 Ginkgo, however, the male nucleus at the time of fusion is relatively 

 small, being less than one-tenth the size of the female nucleus. As in 

 Cycas and Zamia, the male nucleus becomes completely imbedded in 



i'Ml|ifif$lll^^ 



FIG. 67. Formation of ventral canal-cell, fusion of sexual nuclei, and the division of the fusion nucleus 

 in Ginkgo. (After Ikeno.) 



A, apex of central cell of archegonium showing telophase of nuclear division ; a cell-plate, or plasma 



membrane, is formed in the connecting fibers. 



B, egg-nucleus into which a male nucleus (m) has penetrated. 



C, fusion nucleus in prophase of division. 



D, fecundated egg-cell showing fusion nucleus in spindle stage of mitosis ; the mitotic figure lies within 



limits of the nucleus whose membrane seems to be still intact. 



the female before the dissolution of its membrane. Both nuclei are 

 in the resting condition at the time of fusion. 



The spindle of the first karyokinesis following fusion is formed 

 within the nuclear cavity and before its membrane has disappeared 

 (Fig. 67, B, C, D). Nothing is said by Ikeno about being able to 

 distinguish male and female chromatin elements in this division. 



