CHAPTER II. 



^ LINEAR AND SUPERFICIAL AGGREGATES. 



Obviously some of the plants mentioned in the last chapter, 

 such as the oscillarias, are colonies of cells well on the way 

 to complete union into coherent filaments whose elements are 

 attached to each other by considerable areas of the cell-wall. 

 In order clearly to understand this condition, we must con- 

 sider the mode of origin of the individual cells composing 

 the row. 



23. Fission. — Under conditions unknown to us, in the 

 course of its growth a cell may divide by a process known 



Fig. 22A. — ^,one of the final sta^xs in cell-division. The dauphter-nuclei are still 

 connected by kinoplasmic filaments, and across the equatorial plane particles of new 

 cell-wall material are formed. />, the completion of cell-di\'ision ; the dau.crhter- 

 nuclei have rounded off and the new wall is like the lateral walls. Magnified 880 

 diam. — After Strasburger. 



Fig 22B. — Three stages of division in the same cell of an orchid i,J:.pif>actis 

 palustris\. The cell is occupied in great part by vacuoles. In this case the new 

 wall forms first on one side between the nuclei Xa), which gradually travel across 

 to the opposite side (i?), the wall extending until it is complete (6^). Magnified 

 about 380 diam. — After Treub. 



17 



