1898] KARYOKINESIS 1N THE ROOT TIPS OF ALLIUM CEPA 235 
spherical granules, but the attraction sphere is usually not very 
well differentiated. The poles usually lie very close to the wall 
of the cell, giving little or no room for polar radiations (figs. 43, 
44). The figures drawn are not exceptional cases, but scores of 
similar figures can be seen in a single section across the flower 
bud. From a careful estimate, I have a single slide which will 
show several hundred figures of the same nature as those given. 
A careful search was again made for multipolar spindles, and in 
this material they are frequently seen. This is not at all sur- 
prising, however, and is exactly what must necessarily follow 
the sectioning of tissues where the spindles do not all lie in the 
same plane. Especially in thin sections is the pole often cut 
away, giving the appearance that the spindle does not end ina 
single point. Since the spindle threads in Sagittaria pollen 
mother cells are massed into definite bundles, any injury to the 
spindle will produce a multipolar spindle. Such a case is shown 
in fig. 45, where the cell has been crushed at one end, producing 
four apparently separate spindles on the lower side, while the 
upper end is practically intact. The centrospheres appear at the 
two original poles. At the present time, in all the material 
examined by the writer, multipolar spindles seem due entirely 
to two causes : first, to pathological conditions ; and second, to 
injuries of the spindle produced by improper manipulation in 
preparing the sections. The latter may be due toa variety of 
causes. Among the more common of these may be mentioned 
improper killing and treatment of material, sectioning the cells 
into such thin slices that the poles are entirely lost or injured, 
cutting off the poles from the spindles which lie diagonally to 
the plane of the section, and finally, injury by crushing the cells 
in such a manner that the spindle is spread out and torn. 
CoLtumpsus, O. 
EXPLANATION OF PLATES XXI, XXII. 
The drawings have been reduced three-eighths of their original size. They 
were drawn with an Abbé camera, and except in one instance combinations 
of Zeiss and Bausch and Lomb oculars and objectives were used. 
