REPRODUCTIVE ORGANS OF ALG#A.—VAUCHERIA. 395 
circumstance and others, that zoogonidia may be produced in 
Vaucheria in cells divided off for that purpose.) 
Zoospores or Zoogonidia are also not unfrequently formed as 
follows :—The contents of the branch, which has swollen into 
‘a sporangium, contract, and escape as a primordial cell, or one 
without a cell-wall, from a fissure at the apex (fig. 864, A, sp). 
This primordial cell is densely covered by short cilia, and is 
termed a zoospore or zoogonidiwm, which at first rapidly rotates ; 
but it soon comes to rest, when the cilia disappear, and a 
cellulose wall is produced (jig. 864, B). This spore then ger- 
minates by putting out one (fig. 864, c) or two tubes ; or it forms 
on the other side, at the same time, a branched root-like organ 
(fig. 864, D, w). 
Fia. 864. 
Fig. 864. A. sp. Newly formed zoospore or zoogonidium of Vaucheria sessilis 
escaping. 8B. Zoospore at rest after having lost its cilia. c. First stage of 
germination. D. Filament of Vaucheria sessilis producing oogonia, 0g, 09, 
and antheridium,h. w. Hyaline root-like process, forming a sort of 
mycelium. sg. Zoospore, which by germinating has formed the filament. 
After Sachs. 
When sexual reproduction takes place, short branches of 
the thallus or filament, which are in close proximity to each 
other, become transformed into antheridia, h, and oogonia, og, 
og (fig. 864, p). The branch which is to form the antheridium 
is longer than that which forms the oogonium, and gener- 
ally becomes more or less curved, and a division is made about 
halfway from its base. The protoplasm in the upper part 
becomes differentiated into antherozoids, which by means of the 
bursting of the antheridium become free at the same time as 
the rupture of the oogonium takes place. 
The oogonia (fig. 864, D, og, og), of which there are fre- 
quently two near to each other, are somewhat ovoid; they differ 
from the antheridia in containing a good deal of chlorophyll, 
and are separated from the cavity of the thallus or filament by 
a septum situated at their base. The green and granular con- 
tents finally collect in the centre of the oogonium, and colourless 
