No. 449.] STUDIES ON THE PLANT CELL. 



Farmer and Williams, '98). Especially well differentiated asters 

 with centrospheres are present during the mitoses in the ascus, 

 functioning at the end in the peculiar process of free cell 

 formation (Harper, '97). Large centrospheres accompanied by 

 radiations are present during the germination of the spores in 

 certain Hepaticse (Farmer and Reeves, '94, Davis, :oi, Cham- 

 berlain, :03), but are less conspicuously shown in some and arc 

 entirely absent in other phases of the life history. Rcnuukahly 

 large centrospheres with inconspicuous radiations arc known ni 

 the tetraspore mother cell of Corallina (Davis, '98). Ccniro- 

 spheres occur in the basidium (Wager, '94, Mairc, :o2). ( cn- 

 trosomes have been reported during the mitoses in ihc 

 sporangium of Hydrodictyon (Timberlake, :02). Centrosomes 

 have also been described in other types of the thallophytes but 

 we are justified in asking for further work on these bodies 

 since they are generally without raditions and may not have at 

 all the significance indicated. Neither asters, centrospheres or 

 centrosomes seem to be normally present in groups above the 

 bryophytes, nuclear division taking place in these plants by 

 methods, not found in other organisms, which will be described 

 in succeeding sections. 



Vegetative and embryonic tissues of plants above the thallo- 

 phytes present very different conditions from those described in 

 the foregoing paragraph. The centrosphere is replaced by a 

 less definite structure in the form of a kinoplasmic cap which 

 appears at the ends of the dividing nucleus and determines the 

 poles of the spindle (see Fig. 3, /)• They have been described 

 in the cells of vegetative points of several pteridophytes and 

 spermatophytes by Rosen, '93, Hof, '98, and Nemec, '99 and : 01, 

 and in the seta and late divisions in the germinating spore of 

 the liverwort Pellia (Davis, :oi). 



The most highly developed conditions of spindle lorniation 

 are found in the spore mother cells of the bryophytes, pterido- 

 phytes and spermatophytes. Here the nucleus becomes 

 surrounded by a weft of fibrillae which form a kinopkismic 

 envelope probably derived in part from the nuclear memljrane. 

 The fibrillae are at first quite independent of one another or of 

 common centers. Most of the fibrillae enter into the spindle 



