228 ESSENTIALS OF BOTANY 
(0) The shape and size of the larger organ. It is an odgonium, 
containing many nuclei, Within the oégonium is developed an egg, 
which after fertilization becomes an oéspore. 
(c) The shape, size, and thick cell-walls of the mature odspores. 
293. Discussion. — Vaucheria differs greatly from Spiro- 
gyra and from most of the green alge. The filaments are 
not composed of separate cells, but the long branching tube 
is a complex cell with many nuclei. The spore-cases of 
the zodspores, the antheridia, and the archegonia are of 
course additional cells or cell groups growing from the 
filament. 
The process of sexual reproduction in Vaucheria consists 
of the union of the protoplasm of a sperm with that of an 
egg. This union is quickly followed by the development 
of a heavy cell-wall about the fertilized egg. The odspore 
thus formed can resist unfavorable conditions much longer 
than the mature plants could do so. After a resting period 
the spore germinates and produces a new individual. 
Vaucheria belongs to a considerably higher stage of de- 
velopment in the plant world than Spirogyra does. This 
is shown especially by two important points of difference. 
1. Vaueheria has one kind of cell for doing the vegeta- 
tive work of the plant (photosynthesis, etc.) and other kinds 
for reproduction. In Spirogyra all the cells appear alike. 
2. In Vaueheria the gametes are unlike. The sperms 
and the eggs are not only very unequal in size, but they 
differ much in structure and in power of movement, the 
sperms being freely motile while the eggs are stationary. 
In Spirogyra any gamete appears to be like all the others. 
1 These have already been stated in Sect. 288, but as @dogonium is more 
likely to be omitted from a brief course than Vaucheria it seems best to repeat 
the statement. 
