No. 454.] STUDIES ON THE PLANT CELL. 739 



with the breaking down of this structure. The fibers gather 

 into projecting cones presenting a multipolar structure, and two 

 of these, becoming more prominent, absorb the others and thus 

 form a bipolar spindle. 



One of the most recent studies on spindle formation is that of 

 ■Osterhout (: 02) on Agave. This investigation is of especial 

 interest for the extensive experimentation in the technique of 

 fixation. The author proposes a new terminology for the stages 

 of mitosis that need not be presented here. Agave offers a 

 striking peculiarity in the presence of a special membrane 

 around the early stages of the spindle. The fibrillae form inside 

 of this membrane and finally push through it radially into the 

 ■exterior cytoplasm where they gather into cones (Fig. 14/).' 

 The cones separate into two opposite groups with a general 

 parallel arrangement of the fibers and in this manner a bipolar 

 spindle is formed. 



It is becoming possible to make some general statements 

 respecting the methods of spindle formation in the spore 

 mother-cell. Just previous to prophase it is almost always 

 possible to differentiate a region of kinoplasm around the 

 nucleus. This zone has been found to be either granular, e. g., 

 Pellia, Anthoceros (Davis, '99 and :oi), Osmunda (Smith, :oo), 

 Cobea and Gladiolus (Lawson, '98 and :oo), or it presents the 

 appearance of a fibrous reticulum, e. g., Equisetum (Osterhout, 

 '97), Larix (Allen, : 03), Lihum (Mottier, '97 and '98), etc. 

 The latter condition probably develops from the former by the 

 arrangement of granules into fibers and the gradual expansion of 

 a very close network thus formed into a coarser structure. The 

 fibers in this reticulum sometimes surround the nucleus as with 

 a heavy web. They later extend radially into the cytoplasm, 

 partly by the expansion of the network and partly by their own 

 growth and frequently take a radial arrangement. In some 

 instances the spindle fibers are developed very largely within 

 the nucleus from the linin (Passiflora, Williams, '99). They 

 then become gathered into bundles or groups forming the cones 

 which collectively constitute a multipolar figure that is often 

 called a multipolar spindle. By the rearrangement of these 

 cones somewhat parallel to one another, together with more or 



