No. 450.] STUDIES ON THE PLANT CELL. 



435 



method of development. The characteristic appearance of this 

 apparatus is a spindle like figure formed of fibrillae. The poles 

 of the spindle may be occupied by centrosomes or centrospheres 

 or they may be entirely free from such organized kinoplasmic 

 bodies. The essential structures of the spindle are sets of con- 

 tracting fibers which separate the chromosomes into two gn)U|)s 

 drawing them to the poles of the spindle where the dau,>;lUer 

 nuclei are organized. But besides these fibers there are gen- 

 erally present other fibrillae which complicate the nuclear figure. 

 Some of these extend from pole to pole (spindle fibers) others 

 lie outside of the spindle and end freely in the cytoplasm or. 

 attach themselves to chromosomes (mantle fibers), and if centro- 

 somes or centrospheres be present there are likely to be fibers 

 radiating from these centers to form asters. 



The events of mitosis are generally grouped into four periods : 

 (a) Prophase, to include the formation of the spindle and prep- 

 aration of the chromosomes ; (b) Metaphase, the separation of 

 the daughter chromosomes ; (c) Anaphase, the gathering of the 

 daughter chromosomes into two groups which pass to the poles 

 of the spindle ; (d) Telophase, the organization of the daughter 

 nuclei. It is almost needless to say that these periods merge so 

 gradually one into the other that sharp lines cannot be drawn 

 between them. The activities during prophase are especially 

 variable. 



Prophase. — ThQXQ are two types of spindles in plants, (i) 

 those that are formed within the nuclear membrane and (2) those 

 whose fibers originate largely or wholly from kinoplasm outside 

 of the nucleus. Intranuclear spindles have been reported ni a 

 number of groups of the thallophytes. They seem to be the 

 rule in the mitoses of oogenesis in the Peronosporales ( Wager, 

 '96, :oo, Stevens, '99, :oi and :02, Davis, :oo, Miyake, :oi, 

 Trow, :oi, Rosenberg, :03). They are present in Sapn.legnia. 

 Fig. 5a (Davis, -.03). Fairchild ('94) reports them for X'alonia. 

 Farmer and Williams ('98, p. 625) state that the spindle of 

 Ascophyllum is largely intranuclear. Harper (:oo) has not 

 described them for the Myxomycetes, but very little is known 

 about the prophases of mitosis in that group and their presence 

 is quite probable. Timberlake (:02) is not positive whether the 



