216 ELEMENTS OF BOTANY 
On atreshly mounted slide run under the cover-glass iodine solution, 
a little at a time, and note its action on the nucleus. Is any starch 
shown to be present? Ifso, just how is it distributed through the cell? 
273. Reproduction of Spirogyra.— The reproductive process in 
Spirogyra is of two kinds, the simplest being a process of fission 
or cell-division. The nucleus under- 
goes a very complicated series of trans- 
formations, which resultin the division 
of the protoplasmic contents of a cell 
into two independent portions, each of 
which is at length surrounded by a 
complete cell-wall of its own. In Fig. 
151 the division of the protoplasm and 
formation of a partition of cellulose in 
Spirogyra is well shown. The original 
single nucleus has already divided into 
two daughter nuclei. Then a wall 
Fic. 151. Process of Cell. begins as a sort of ring or diaphragm 
Multiplication in a Species Which at length completely separates 
of Spirogyra. (x 230.) the two nuclei. The original cell has 
At n,n the daughter nuclei are = NOW become two. 
seen on either side of the Another kind of reproduction, 
newly forming partition wall namely by conjugation, is found in 
rma arent Me IN Spinggrn. This proces in ite so 
of chlorophyll ch whieh lines plest form is found in such unicellu- 
thecellavall. Sectionsofthis lar plants as the desmids (Fig. 152). 
bandareseenatvariouspoints — Two cells (apparently ae alike) 
s. Threadsof protoplasm join Gome jn contact, undergo a thinning- 
it to the nuclei. i pete . 
down or absorptive process in the cell- 
walls at the point of contact, and finally blend their protoplasmic 
cell-contents, as shown in the figure, to form a mass known as a spore, 
or more accurately a zygospore, from which, after a period of rest, 
a new individual develops. In Spirogyra each cell of the filament 
appears to be an individual and can conjugate like the one-celled des- 
mids. It is not easy to watch the process, since the spore-formation 
takes place at night. Tt is possible, however, to retard the occurrence 
of conjugation by leaving the Spirogyra filaments in very cold water 
over night, and in this way the successive steps of the conjugating 
