No. 450.] STUDIES ON THE PLANT CELL. 441 



It would be interesting if two types of spindle formation were 

 present at opposite poles of the same nucleus and further inves- 

 tigation of this subject is much to be desired. The mitoses in 

 the central cell of Pinus (Ferguson, :oib, Chamberlain, '99, 

 and Blackman, '98) and Picea (Miyake : 03a) show spindle for- 

 mation from accumulations of fibrillae outside of the nucleus but 

 without conspicuous polar caps. Still more striking than the 

 irregular spindle of Murrill in Tsuga, described above, is Miss 

 Ferguson's (:oia) account of the mitosis in the generative cell 

 of the pollen grain of Pinus. The spindle here begins to develop 

 as a cap-like accumulation of kinoplasm below the nucleus. The 

 fibers enter the nuclear cavity and in cooperation with a nuclear 

 reticulum form a system of fibers that extend through the 

 nuclear cavity to the inner side of the nuclear membrane 

 beyond. This portion of the nuclear membrane persists until 

 after metaphase so that one pole of the spindle is found wholly 

 within the nucleus while the other is external and of unques- 

 tioned cytoplasmic origin. Coker, : 03, regards the spindle which 

 differentiates the nucleus of the ventral canal cell in Taxodium 

 as- almost wholly of nuclear origin and the chromosomes as 

 derived largely from the nucleolus. There are evidently some 

 interesting complications in this form which deserve further 

 study. 



It should be noted that whenever spindles are formed in con- 

 nection with centrosomes, centrospheres or kinoplasmic caps that 

 the fibers have a definite region of attachment from which they 

 extend into the nuclear cavity. Such regions constitute a sort 

 of anchorage for the spindle fibers. In this respect the physi- 

 ological side of the process of spindle formation in these forms 

 is quite similar to that of the animal kingdom and in sharp 

 contrast to other methods that are found in higher plants, which 

 will now be considered. 



When spindles are formed after the second method, i. e., 

 by independent fibrillae making up a network around the nucleus, 

 there is an abrupt change in the method of development. 

 The kinoplasm becomes distributed around the nucleus as an 

 investing layer and shows no inclination to gather into centers 

 such as kinoplasmic caps or centrospheres. There is developed 



