BOT.-VOL. II.] OSTERHOUT -AGAVE. 1*J\ 



6. Bipolar Stage. 



Strictly speaking, there is not, as a rule, a bipolar stage, 

 since the fusion does not become complete but remains in 

 the stage shown in fig. 29. It is not uncommon to find the 

 fusion complete at one end but not at the other, and in 

 some cases the spindle may become truly bipolar. 



GENERAL CONSIDERATIONS. 



The spindle formation of the first mitosis of Agave, as 

 set forth above, differs markedly from anything hitherto 

 described. The formation of a spindle wall which com- 

 pletely encloses the spindle during the genetic stage is 

 unique; and the origin and development of the genetic 

 fibres is peculiar. 



The spindle wall would seem to be a structure of great 

 physiological importance, comparable in its functions with 

 the nuclear wall and the limiting layer of the cytoplasm. 

 Its special function appears to be to segregate the important 

 process of spindle formation, thus carrying the division of 

 labor in the cell to a point otherwise impossible. Its pres- 

 ence therefore indicates a high degree of cell organization. 



In appearance and mode of origin the spindle wall resem- 

 bles the nuclear wall; its close relation to the nucleus is 

 shown by its origin and development; it persists, however, 

 after the nuclear wall has disappeared, and may then per- 

 haps assume some of its functions. It is either in actual 

 contact with the nuclear wall during the genetic stage or is 

 constantly connected with it by the genetic fibres; on the 

 other hand, it early forms connections with the limiting 

 membrane by means of the exterior fibres. The relations 

 existing between the kinoplasm and the limiting membrane 

 have recently been emphasized by Strasburger (1900, p. 

 144 et seq.), who calls attention to the fact that in many 

 forms the kinoplasmic fibres can be traced to this membrane 

 and that the spindle is in many cases inserted on it. Agave 

 offers direct confirmation of these statements. 



It is possible that there may be some homology between 



(2) May 2, 1902. 



