ULTRASTRUCTURE OF CELL-DIVISION IN THE FUSIFORM CELLS OF THE VASCULARCAMBIUM OF ROBINIA-PSEUDOACACIA

The ultrastructure of periclinally dividing fusiform cells was studied in the vascular cambium of Robinia pseudoacacia. Fusiform cell divisi on begins in April at Madison, Wisconsin, when the cambial cells still have many characteristics of a dormant cambium. Soon afterward, the c ambial cells acquire the appearance typical of an active cambium. Sequ ential phases of the microtubule cycle were documented: cortical micro tubules bordering the cell wall during interphase, perinuclear microtu bules preceding formation of the mitotic spindle, spindle microtubules , and phragmoplast microtubules. A preprophase band of microtubules wa s not encountered. An extended phragmosome was not encountered in peri clinally dividing fusiform cells. During cytokinesis, the phragmosome is represented by a broad cytoplasmic plate which precedes the develop ing phragmoplast and cell plate as they migrate toward the ends of the cell.