264 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



sarily fatal to the assumption of dynamic centers." Gallardo 

 attempts to show how the tilting of the spindle may cause an 

 apparent crossing of fibers which really do not cross. The trained 

 cytologist will, however, hardly accept this as proof that there is 

 no crossing of fibers in the cell. Wilson objects to the dynamic 

 interpretation on the ground that it cannot explain the tripolar 

 figures. Hartog (29) has made, perhaps, the most careful 

 attempt to correlate the kinoplasmic fibers with lines of force. 

 He concludes that they are the result of a force which is "analogous 

 to magnetism, and still more to statical electricity." Their 

 behavior is due to their relative conductivity: the fibers, mem- 

 branes, and chromosomes being of high conductivity. 



Still more recently, interesting studies on the chemical changes 

 in the cell incident to cell-division have appeared. Robertson 

 (55) suggests that cholin is formed as a by-product about the 

 daughter nuclei, and diffuses in all directions, hence reaching its 

 maximum concentration in the equatorial plane. This causes a 

 diminution in surface tension along the equator and hence the two 

 hemispheres round up against each other. That the cleavage fur- 

 row Is due to decreased surface tension is also held by Loeb and 

 Lillie; but McClendon and Biitschli contend that it is due to 

 increased surface tension at the equator, which brings about a 

 constriction in that region. McClendon (46) has performed 

 many unique experiments in support of his view; these have been 

 otherwise interpreted by Robertson, and the latter has devised ex- 

 periments to demonstrate the opposite contention; with the result 

 that there is still a question as to which condition does exist. 



/. Terminology of cell-division 

 In spore-mother-cells each nuclear division may be at once 

 followed by cell-division, or cell-dhislon may take place after the 

 four nuclei have been formed. There has been some confusion 

 in the terminology heri'. Strasburger referred to the latter process 

 at first by the term "simultan" (67a), and later (67/) by the 

 word " Viertheilung." The same writer refers to the process of 

 partition in Fiiciis and Sphacelaria as simultaneous, as opposed 

 to pnjgresslve. It seems that this term sunultaneous should be 

 restricted to the tyi)e of cell-(li\lsl()n In these brown algae, meaning 

 that the process of dulsion is at tlii' saini- stage of (k'xclopment 



