74 MARGARET C. FERGUSON 



passage of the one-half chromosomes to the poles has not been 

 observed. Resting nuclei are formed during the telophase of 

 the mitosis, and a cross wall divides the mother-cell into two 

 compartments (fig. 138). 



From the foregoing it is evident that the first division which 

 takes place in the macrospore-mother-cell is heterotypic in 

 nature, and agrees in all essentials with the primary mitosis 

 within the microspore-mother-cell. This is in accordance with 

 the conclusions reached by all other investigators who have 

 recently studied the tetrad divisions occurring within the ovules 

 of various Phanerogams. 



Second Division of the Macrospore-mother-celL Beginning 

 with the telophase of the first division considerable variation 

 may occur in the subsequent steps in the formation of the axial 

 row. A cell-plate is always formed between the daughter- 

 nuclei though it may remain very delicate, consisting of little 

 more than a condensation of the ectoplasm. The daughter- 

 cells may be very similar in appearance, excepting that the 

 lower one is usually the larger, and in such instances both nuclei 

 enter the resting stage, presenting a clear, definite reticulum 

 (figs. 138, and 141). More often, however, the lower cell is 

 much larger than the upper one and the nucleus of the upper 

 cell does not enter into the complete resting stage, but early 

 shows signs of disintegration. The chromosomes may unite to 

 form a spireme as usual, but development may then cease 

 without the organization of a network, and the diffuse reaction 

 of the nucleus to stains shows that disintegration has begun 

 (figs. 139, 140). 



I have but a single preparation showing the second division 

 of the macrospore-mother-cell, and I can therefore offer no con- 

 clusions of any value regarding the nuclear phenomena accom- 

 panying the mitosis. From this figure it appears that the 

 spindle originates as a multipolar diarch as in the first division, 

 and both nuclei in this instance are dividing at the same time. 

 During the initiation of the spindle the chromosomes are short 

 and thick, somewhat irregular in outline, and apparently in the 

 forms of U's, V's and rings. The reduced number of chromo- 

 somes occurs in both of the dividing nuclei (fig. 142). 



