3l6 LESTER -W. SHARP 



parts lying in a favorable plane. In other parts the double nature may be 

 revealed through focusing. The occurrence of free ends not in the planes 

 passed through by the knife again makes it clear that no continuons spirem 

 is formed. A small détail from such a nucleus is shown in fig. 18. Besides 

 the connections between the longitudinal halves of the same chromosome 

 there are numerous fine ones between neighboring chromosomes which lie 

 close together. It is probable that many such anastomoses are formed at a 

 late stage as the resuit of contact of the semi-fluid bodies, and are not ne- 

 cessarily retentions from earlier stages. 



The fuUy formed spirem threads still show the split very clearly. 

 Fig. 19 represents a nucleus from the peripheral portion of a root fixed in 

 Flemming's strong solution. In this région where the fixation is good there 

 is no difficulty in recognizing the présence of the split. In the inner por- 

 tion of the root it is often not made out at ail, since this solution, as stated 

 by Flemming (82) himself, fixes very poorly the inner cells. The fixation 

 of interior cells of roots killed in Benda's solution, though not as good as 

 in peripheral cells, is as we hâve seen much better than in similar cells 

 treated with the solution of Flemming. Such an inner cell fixed in Benda's 

 fluid is shown in fig. 20. Hère the split, though obscure in parts, is at 

 once seen to be présent, being especially évident at free ends. The eut ends 

 at the right in the figure show that the halves are pressed or hâve flawed 

 together. This seems to be due for the most part to the action of the fixing 

 agent, since in peripheral cells, especially those treated with Benda's solu- 

 tion, such an obscuring of the split does not occur. Although the halves 

 corne to lie very close to each other at this time because of their shortening 

 and thickening, they do not fuse. 



The polar caps now appear, first as thin convex masses of clear 

 » kinoplasm " which quickly become more conical and in which the spindle 

 fibers seem to difïerentiate, fig. i9, 20. The whole nucleus contracts rather 

 rapidly after the manner described by Lawson for Smilacina [lia] and 

 several other plants including Allium (11/'). But it is important in this 

 connection to note that in the case of Vicia the fibers are seen differentiat- 

 ing in two opposed régions before the nucleus begins its contraction. 

 Consequently Lawson's theory regarding the origin of the spindle is not 

 upheld by the présent investigation. 



When the contraction is at its height the chromosomes are very closely 

 packed and their halves becorne tightly pressed together. Fig. 21 shows 



