40 MARGARET C. FERGUSON 



in the reduced number, become apparent. These segments are 

 at first irregular and jagged in outline showing distinctly the points 

 at which each has separated from neighboring segments, but they 

 gradually diminish in size and become more regular in contour. 

 The chromosomes thus formed are in the form of X's, Y's, V's, 

 U's, L's, parallel rods, rings, and indefinitely-shaped bodies. 

 Each segment consists of two chromosomes fused side by side. 



The spindle-fibers arise both from the nuclear membrane 

 and from the cyto-reticulum. The achromatic figure may 

 originate as a multipolar polyarch of three poles or as a broad 

 multipolar diarch spindle. At the close of the prophase of the 

 heterotypic division the spindle has become sharply bi-polar 

 and its extremities may be imbedded in the ectoplasm or they 

 may end blindly in the cytoplasm. 



The chromosomes are separated at the equatorial plate with 

 difficulty giving the appearance of a plastic substance under 

 tension. Their separation may be so delayed that the daughter- 

 chromosomes stretch from pole to pole. They ordinarily have 

 the form of V's or U's during the anaphase of the mitosis, but 

 other forms are not infrequent. The first division effects a 

 longitudinal splitting of the chromosomes into daughter-seg- 

 ments of the same form as the parents. 



A resting nucleus is established at the close of the first mitosis 

 but the daughter-nuclei are not separated by a cell-wall. The 

 daughter-reticulum soon gives rise to a more or less spirally 

 coiled chromatic band which loops itself at the equatorial plate 

 and splits longitudinally before segmentation. 



The chromosomes have the form of U's and are oriented at 

 the equatorial plate in two rows with their free ends touching 

 and the bent portion of each segment directed towards the poles, 

 the complete fission of the segments having been completed 

 before their migration to the poles begins. The writer inclines 

 to the view that these are the half chromosomes of the daughter- 

 pairs which were separated in the first division. If this hy- 

 pothesis be correct, the homotypic mitosis in Pinus effects a 

 true or qualitative reduction of the chromosomes. 



The wall of the microspore-mother-cell increases markedly 

 in thickness and its protoplasmic contents is separated into four 



