DAMPING OFF. 239 



end of a hypha or short branch, which continues until the spheri- 

 cal body is about 1 8/^-2 5/Jt in diameter. During its growth in size 

 the protoplasm which fills the interior is supplied by the support- 

 ing hypha or oogoniophore, without, however, emptying any 

 portion of the latter structure. When the oogonium has reached 

 its full size, a septum, or partition wall, is formed cutting off its 

 protoplasm from that of the stalk or oogoniophore. At this time 

 the wall of the oogonium is thin and the protoplasm finely granu- 

 lar, though distinctly so, and completely fills the interior of the 

 oogonium. The wall now increases somewhat in thickness, but 

 remains colorless. 



The egg cell of the oogonium is now soon differentiated, and 

 in most cases, except where parthenogenisis takes place, is prob- 

 ably influenced by the development of the antheridium. The 

 finely granular protoplasm of the oogonium becomes coarser and 

 is gradually collected into numerous small irregularly rounded 

 masses. At the same time all of the coarsely granular protoplasm 

 contracts from the wall of the oogonium and moves toward the 

 center forming there a rounded central mass somewhat less in 

 diameter than that of the oogonium, being 14^ 18// in diameter. 

 This central sphere of coarsely granular protoplasm is termed the 

 oosphere, or egg cell, and is really an unfertilized egg, the recep- 

 tive cell of the oogonium. Between this egg cell and the wall of 

 the oogonium is a space filled with a nearly clear, but finely 

 granular and homogeneous fluid called the periplasm. At this 

 stage there is no wall surrounding the egg cell and it is ready to 

 be fertilized. 



Antheridia. The sole purpose of the antheridia is to supply 

 the fertilizing element for the egg cell, and the antheridium is 

 sometimes termed the supplying gamete, while the oogonium is 

 termed the receptive gamete. The antheridia are of two kinds, 

 stalk antheridia and branch antheridia. A stalk antheridium is 

 formed from a section of the oogoniophore by the formation of a 

 partition wall in the hypha cutting off an elongated cell one end 

 of which is thus in contact with the wall of the oogonium, and 

 its contents are only separated from those of the oogonium by the 

 wall of the latter. This is the simplest of the two forms of the 

 antheridia. 



