ALGAE. CHARACEAE^ 



59 



The oogonium (nucule) when fully grown and ready for fertilisation is of a longer or 

 shorter ellipsoidal form, and is supported on a short cell serving as a stalk (the 

 pedicel-cell), which is visible externally only in Nitella and consists of an axile row of 

 cells closely invested with an envelope of five spirally twisted tubes. The whole may 



FIG. 38. Development of the antheridia in Nitella flexilis. At Ft, C, and JJ the 

 protoplasm has been contracted by glycerine. 



be described as a metamorphosed shoot, but this does not mean that the oogonium 

 actually originates in the transformation of a shoot. The pedicel-cell answers to the 

 lowest intemode of a shoot and bears a short nodal cell, from which the envelope-tubes 

 arise like a whorl of leaves. Above the nodal cell rises the peculiarly formed apical 

 cell of the shoot, which is large in proportion to 

 the other parts and ovoid. At its base imme- 

 diately above the nodal cell a short hyaline cell 

 is divided off at an early stage in Chara ; its 

 place is taken in Nitella by a disc-shaped group 

 of such cells, which Braun has called the ' Wend- 

 ungszellen.' The large apical cell of the oogo- 

 nium is filled with protoplasm and a number of 

 oil-drops and starch-grains, but its apical region, 

 the apical papilla, contains pure hyaline proto- 

 plasm. The tubes of the envelope,, which are 

 rich in chlorophyll, project above the apical 

 papilla and support the crown, which is com- 

 posed of five larger cells in Chara, of five pairs 

 of small cells in Nitella : these cells were divided 

 off by transverse septa from the enveloping tubes 

 at an early period. Above the apical papilla and 

 beneath the crown, which constitutes a compact 

 lid, the five enveloping tubes form the neck, which 

 encloses a narrow cavity, the apical cavity ; this 

 is inversely conical above the papilla and grows 

 narrower upwards, because the five segments of 

 the neck project inwards and form a kind oT dia- 

 phragm, through the central and very narrow 

 opening of which communication is maintained 

 with the upper roomy portion of the apical cavity. The cavity is closed above by the 

 crown, but five lateral fissures appear between the neck-portions of the five tubes at the 

 time of fertilisation and thus an opening is made to the outside ; through these fissures 

 the spermatozoids find an entrance into the apical cavity, which is filled with hyaline 



FIG. 39. More advanced state of the antheridium of 

 Nitella flexilis magn. about 500 times. 



