222 ESSENTIALS OF BOTANY 
282. Discussion. — Spirogyra resembles Oscillatoria 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 Oseillatoria, con- 
Fic. 156. Process of Non- 
Sexual Reproduction in aSpe- 
cies of Spirogyra. (x 280.) 
At n,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 chlorophy]1 
ch which lines the cell-wall. 
Sections of this band are seen 
at various points s. Thredds 
of protoplasm join it to the 
nuclei. 
| sists of a process of cell-division, 
shown in Fig. 156. 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 
1 See Bergen and Davis’ Principles of Botany, Sect. 199. 
