88 Practical Plant Biology. 



The branches are of two kinds and are usually formed close to- 

 gether. The oogonia are short rounded branches the cavity of 

 which is separated from that of the ccenocyte by a transverse 

 wall. The branch or oogonium is egg-shaped with an obliquely 

 placed apical prominence. The cell-wall covering this prominence 

 becomes gelatinous and soft during the later stages of the de- 

 velopment of the oogonium. The oogonium is filled with a mass 

 of protoplasm the ovum. In the centre of the ovum a nucleus 

 may be seen. Round the latter, in the peripheral layers, are 

 crowded great numbers of chloroplasts which make the whole 

 oogonium dark in colour. In the immediate neighbourhood of 

 its apical prominence or beak the chloroplasts and other granules 

 are absent, and the protoplasm at this spot is transparent and 

 colourless. This colourless region of the ovum is called the 

 receptive spot. The oogonium arises as a small swelling on the 

 side of a branch of the ccenocyte. Cytoplasm carrying nuclei 

 and chloroplasts moves into this swelling or bulge. Subsequent 

 growth converts this excrescence into a very short, thick cylindrical 

 branch and a cross partition cuts it off from the rest of the 

 ccenocyte. In some species of Vaucheria, just before this partition 

 is completed, all the nuclei save one retire into the ccenocyte. 

 In the species of Vaucheria where they remain in the oogonium, 

 after it has been isolated by the partition, all the nuclei except 

 one undergo a process of disintegration. In either case only one 

 nucleus survives in the oogonium. The latter now begins to 

 swell and takes on its mature egg-shaped form. 



Simultaneously with the oogonium, the antheridium is formed 

 and usually in close proximity. The antheridium is a slender, 

 curved, cylindrical branch. Protoplasm from the supporting 

 ccenocyte moves out into this branch as it grows. When its 

 length is about 4-8 times its diameter and the antheridium has 

 become much more curved, a transverse septum of cellulose is 

 formed in it dividing off a terminal portion. This portion con- 

 tains a large number of nuclei and chloroplasts. The former 

 collect in the central region while the chloroplasts mass at the 

 periphery. The central mass of protoplasm now breaks up into 

 a large number of tiny masses each containing a nucleus and 

 carrying two cilia. The cilia are placed far apart and diverge 

 from one another. These very small motile cells are the sperms. 

 As they develop they take on a dancing motion. The tip of the 

 antheridium soon opens and the sperms are ejected into the sur- 

 rounding water. Some of the outer protoplasm is thrown out with 

 them and some remains in the antheridium. 



