CHAPTER III. 

 FILAMENTOUS ALG/E. 



Obviously some of the plants mentioned in the last chap- 

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



way to complete union into co- 

 herent filaments whose elements 

 l-ik:y^S£:'9\ /-jisiHvVSiL-Ji, are attached to each other by con- 

 siderable areas of the cell-wall. 



In order clearly to understand this 

 condition, we must consider the mode 

 of origin of the individual cells composing 

 the row. 



21. Fission. — Under conditions mostly 

 unknown to us, in the course of its growth 

 a cell may divide by a process known 

 as fission . The material of the nucleus 

 passes through a complex series of 

 changes and separates into two parts. 

 In a plane between these daughter-nuclei particles are deposited to form 

 a cell-wall {A, fig. 14). In this way a single one-celled plant of Pleiiro- 



FiG. 14. — A, one of the final stages 

 in cell-division. The daupliter- 

 nuclei are still connected by fila- 

 ments, and across the equatorial 

 plane particles of new cell-wall 

 material are formed- B, the com- 

 pletion of cell - division ; the 

 daughter-nuclei have rounded oil 

 and the new wall is like the 

 lateral walls. Magnified 880 diam. 

 — After Stiasburger. 



Fig. 15.— Diagrams of cell-division. A, division of a spherical cell into two hemi- 

 spherical cells, «, bf by the wall i. B, the same after further division in planes 2, 

 2, 3, parallel to i. a has divided by wall 2 into a' and another cell which has again 

 dividedby wall 3 into rt". a", h has divided into b', b\ the inner of which has 

 elon^ted preparatory to a division into b" , b", as by wall 3. C, fig. A, after a second 

 division, by wall 2, at right angles to i. 



16 



