NUCLEAR DIVISION. 



the development of the karyokinetic spindle in both vegetative and 

 reproductive cells agrees essentially with that described for Dictyota. 

 In the diatoms the development of the spindle as described by 

 Lauterborn ('96) is singular and without parallel in the plant king- 

 dom. According to this author, the spindle develops directly from 

 the centrosome by a division of the same or by budding. We shall 

 refer to this phenomenon beyond in the section dealing especially with 

 the centrosome. In the red algae the development of the karyokinetic 

 figure is known somewhat in detail only in Corallina officinalis. In 

 this plant, Davis ('98) finds that the spindle arises through the agency 



K 



FIG. 3. Second mitosis in tetraspore mother-cell of Dictyota. 

 H-K, prophase, showing origin of spindle. L, a nearly mature spindle. 



of centrospheres which undergo a great change in size during mitosis. 

 The persistence of these bodies was not followed from one cell genera- 

 tion to the next. The paucity of our knowledge of nuclear division 

 in the red algae precludes any further mention of the subject in this 

 group of plants. So far as is known to the author, no centrospheres 

 or centrosomes have been authentically observed in the green algae. 



ERYSIPHE COMMUNIS. 



For the fungi, the most accurate and complete account of karyoki- 

 nesis is to be found in the classical work of Harper ('97) on certain 

 Ascomycetes. As an illustration of the process in this group of fungi, 

 which is probably best known cytologically, a brief account of mitosis 

 will be given as described by Harper in the ascus of Erysiphe 

 communis. 



