BOT— Vol. II.] OSTERHOUT— AGAVE. 275 



It is proposed that the stages of spindle formation be 

 characterized as 



(i) Progenetic 



(2) Genetic 



(3) Stellar 



(4) Fascicular 



(5) Bipolar. 



The progenetic stage may be defined as the stage preced- 

 ing the genetic, and in which preparation for the genetic 

 stage goes on in the cytoplasm ; the region of the cytoplasm 

 in which this takes place and from which the genetic layer 

 arises may be called the progenetic layer. 



The genetic stage lasts from the first appearance of the 

 genetic Jibres (i. e., the spindle-forming fibres) to the com- 

 plete development of the spindle cones and the disappear- 

 ance of the nuclear wall. When these processes do not 

 take place simultaneously, it is to be understood that the 

 genetic stage does not end until both are completed. The 

 layer containing the genetic fibres is called the genetic layer . 



The stellar stage lasts from the end of the genetic stage 

 to the separation of the cones into two (more or less oppo- 

 site) groups, and the commencement of the parallel 

 arrangement of the fibres. 



The fascicular stage lasts from the end of the stellar 

 stage to the complete fusion of the cones (to form the 

 bipolar spindle), or, where this does not occur, to the 

 arrival of the daughter chromosomes at the poles. 



The bipolar stage lasts from the end of the fascicular 

 stage to the complete disappearance of the poles. 



