222 



ESSENTIALS OF BOTANY 



282. Discussion. — Spirogyra resembles Osoillatoria in 

 consisting of filaments composed of a row of cells each of 

 which is an individual plant. Its structure is, however, 

 of a much higher character since the chlorophyll-containing 

 material is in distinct bands, the pyrenoids form a special 



starch-making apparatus, and 

 there is a well-defined nucleus. 

 Spirogyra has a sexual as well 

 as a non-sexual mode of repro- 

 duction, while in Oscillatoria 

 the reproduction is always non- 

 sexual. 



Asexual reproduction, in 

 Spirogyra as in Oscillatoria, con- 

 sists of a process of cell-division, 

 shown in Fig. 166. The nu- 

 cleus divides into two daughter 

 nuclei, and the protoplast be- 

 comes divided into two portions. 

 A new partition- wall begins as a 

 sort of ring, or diaphragm, and 

 at length completely separates 

 the two new nuclei. The pro- 

 cess of cell-division in Spirogyra 

 is much more complicated than 

 in Oscillatoria, as in the former plant the nucleus goes 

 through a remarkable series of changes (mitosis) ^ previous 

 to the formation of the daughter nuclei shown in Fig. 156. 

 Sexual reproduction consists in the union of two appar- 

 ently similar cells belonging usually to different filaments. 

 A sexual cell which unites its contents with those of 



Fig. 156. Process of Non- 

 SexualEeproduction in aSpe- 

 cies of Spirogyra. (x 230.) 



At ra, n the daughter nuclei are 

 seen on either side of the newly- 

 forming partition wall w. By 

 its growth the partition pushes 

 inward the band of chlorophyll 

 chwhich lines the cell-wall. 

 Sections of this band are seen 

 at various points 6. Threads 

 (Of pKOtoplasm join it to the 

 nuclei. 



1 See Bergen and Davis' Principles of Botany, Sect. 199. 



