120 BOTANY. 
252. The reproduction of desmids takes place by fission 
and by union; that is, asexually and sexually. In the first, 
the neck uniting the two halves of the cell 
elongates and becomes divided by a trans- 
verse partition, so that instead of the original 
Fig.52.—Ades- Symmetrical cell there are now two exceed- 
midin processof . . . 
fission. Highly ingly unsymmetrical ones (Fig. 52); these 
magnified. : 
grow by the rapid enlargement of the new 
and small halves; eventually the two cells become sym- 
metrical, by which time they have separated. This pro- 
cess may be repeated again and again. 
253. In the sexual process each of two cells which are 
Fie. 53.—Sexual reproduction of a desmid (Cosmarium menenghinii). a, front; 
b, end; c, side view of the adult plants; d. two cells conjugating; e, young rest- 
ing spore formed; /. ripe resting spore, with spiny wall—the four halves of the 
git cells are empty; g, the resting spore germinating after a period of rest; 
. 
the young cell escaped from resting spore; 7, young cell dividing, showing 
two new plants, similar to a, placed crosswise in the interior of the cell. Magni- 
fied 475 times. 
near one another sends out from its centre a tube, which 
meets the corresponding one from the other (d, Fig. 53). 
At the point of meeting the two tubes 
swell up hemispherically, and finally, by 
the disappearance of the separating wall, 
the contents unite and form a rounded 
dentia” Gilets, Testing spore (e), which soon becomes 
Highly magnified. coated with a thick wall (f). After a 
longer or shorter time the resting spore may germinate, 
