BOT.-VOL. II.] OSTERHOUT— AGAVE. 273 



spindle wall) could hinder or altogether prevent the expan- 

 sion of the nucleus and so eliminate the weft stage. The 

 osmotic pressure of the genetic layer, if equal to or slightly 

 greater than that of the nucleus, would bring about this 



result. 



The exterior fibres do not seem to be essentially different 

 from the genetic fibres save that, being outside the spindle 

 wall, most of them take no direct part in the formation of 

 the spindle. Both kinds of fibres seem to be similar to the 

 radial kinoplasmic fibres of Equisetum. Some of the exte- 

 rior fibres form fibre cones in much the same way as in 

 Equisetum, but these structures are, in the case of the first 

 mitosis of Agave, merely temporary. 



The formation of the spindle cones is peculiar on account 

 of the part played by the exterior fibres. According to 

 Belajeff (1894), the spindle cones of Larix are formed in 

 connection with certain fibres which extend from the gene- 

 tic layer to the cell wall. In this respect the process 

 resembles that which occurs in the first mitosis of Agave, 

 but the fibres do not group themselves to form the spindle 

 cones in the manner described by Belajeff. 



While the method of spindle formation in the first mitosis 

 stands unique, that of the second mitosis recalls the origin 

 of the spindle in the spore-mother-cells of Equisetum 

 (Osterhout, 1897), with which it agrees in most of its prin- 

 cipal features, e. g., in the origin of the genetic fibres in 

 contact with the nuclear wall, their radial arrangement and 

 outward growth into the cytoplasm, their assemblage in 

 groups accompanied by a fusion of their free ends to form 

 cones, and, finally, the fusion of these cones to form the 

 spindle. In Equisetum, however, there is at first a modi- 

 fied weft stage of which no trace is seen in Agave. This 

 agreement with Equisettmi is the more surprising since the 

 relationship between the two plants is so remote, while the 

 spindle formation of the immediately preceding mitosis of 

 Agave presents such profound differences. 



Investigations on spindle formation, though as yet but 

 few in number, have revealed great diversity, especially in 



