344 PHARMACEUTICAL BOTANY 
of cellulose within which is to be found a thin film of ectoplasm. 
One or more spirally shaped chromatophores will be seen directly 
within this area. Each chromatophore contains chlorophyll 
and a number of pyrenoids. In the center of the cell the nucleus is 
found. Fine strands of protoplasm hold it in place and run out 
to the ectoplasm. 
Under favorable circumstances the cells of Sperogyra increase 
rather rapidly in length. Abnormally long cells are not seen, 
however, because the elongating cells speedily divide, forming 
two daughter-cells. Under the best of conditions, division may 
Fic. 249.—Spirogyra longata. Portion of a monoecious filament showing two 
adjacent cells in the early stages of conjugation. This type of conjugation is 
called lateral. Ladder-like or scalariform conjugation of dioecious filaments is shown 
in figure 248. Note the pulsating or contractile vacuoles. (From Gager, after 
Lloyd.) 
occur every night. In this way the filaments are rapidly made 
longer. Sooner or later they break and in this way the plant 
multiplies. | 
Spirogyra has also a process of sexual reproduction known as 
conjugation. This process occurs normally from March to 
June and July, but can be induced in the laboratory by allowing 
the water in the vessel in which it is growing to slowly evaporate. 
Two filaments arrange themselves side by side, and the cells lying 
opposite each other undergo internal changes so as to form gametes 
or sexual cells. Each gamete-containing cell is called a game- 
tangium. Each gametangium protrudes a process or lateral 
branch. The tips of these fuse upon meeting each other and 
form a conjugation tube or connecting tube. ‘Then the protoplast 
(gamete) of one cell passes over and coalesces with that in the cell 
