228 INTRODUCTION TO BOTANY 
Another kind of reproduction may occur at the same time 
that zodspores are being formed, though it usually occurs at 
other times. Upon the sides of the plant special short branches 
are formed. Two kinds of branches arise near one another 
(fig. 178). One is short and irregularly spherical, and has a 
beak. This branch forms one large cell within it. The other 
branch is longer, somewhat coiled, and has a terminal cell that 
is cut off by means of a cross wall. In the terminal segment 
many small cells are formed. Through a small opening in 
the tip of this coiled 
branch these cells es- 
cape, some of them 
entering the beak of 
the other branch and 
one of them uniting 
with the large cell. 
This union forms a 
Fic. 178. The sexual reproductive structures “Pore which proceeds 
of Vaucheria (V. sessilis) to develop a heavy 
0, odgonia; A, antheridium. Note the opening in protecting wall. After 
the antheridium for exit of sperms, and in the , aD . Es 
oogonia for their entrance to the large eggs. e period of rest this 
Greatly enlarged spore germinates and 
produces a new plant.! 
If this spore had been formed by the union of similar gam- 
etes, as In Spirogyra, we should have called it a ZY@OSpore ; 
but it is formed by the union of gametes that are very unlike, 
— one large gamete (the eyy, or vdsphere) and the other a small 
gamete (the sperm),—and the resulting spore is called an 
odspore, which means “egg spore.” When similar gametes 
unite to form a zygospore, the process is called conjugation, 
but when dissimilar gametes unite to form un odspore, the 
process is called fertilisation. The special sex organ which 
produces the sperm is the wutheridinm, or sperm case, and that 
which produces the egg is the vdyouinin, or eve case. 
To ran Tracner. No attempt is made to present the difficult and tech- 
nical questions relative to the alternation of generations in the thallophytes. 
