CHARA FRAGILIS. 309 



treatment with iodine. At their hinder end the spermatozoids 

 are somewhat thickened, and enclose glistening granules. The 

 spermatozoids progress by simultaneous vibratory movement and 

 rotation around their axis. The whole preparation swarms with 

 spermatozoids, since the number produced in a single antheridium 

 has been estimated at about 30,000. The antheridia tend to 

 open spontaneously in the early morning. The spherical curva- 

 ture of the shields diminishes notably, so that they separate from 

 one another, and this tendency occasions the springing open of 

 the organ. The spermatozoids are wont to swarm for some 

 hours. 



Oogonia of Chara. In order to learn the structure of the 

 nucule or oogonium, we preferably first study it in those stages 

 of development in which it is still cylindrical and transparent. 

 The antheridium found under it is then fully formed, and the 

 oogonium itself begins to be somewhat brownish. In such an 

 oogonium can be seen an elongated central cell or oosphere, 

 densely filled with finely granular protoplasm. It is borne upon 

 two flat internal cells, of which the upper is distinguished as the 

 " Wendungszelle " (v), and the under is a nodal cell (no), and 

 upon a short stalk-cell (po). This last is seated upon the nodal 

 cell (na) which bears the antheridium. The central cell of the 

 oogonium is sheathed by five tubular sacs, which arise from the 

 nodal cell (no). These sacs run spirally around the central cell, 

 and end above in the so-called crown (c). The five cells of this 

 latter are cut off by partition walls from the investing sacs. If 

 the crown consists thus of but five cells, we can at once determine 

 our plant to be Chara, while the other genus of Characeae, 

 Nitella, possesses a ten-celled crown, consisting of five pairs 

 of superposed cells the result of a subsequent division of each of 

 the five cells. In the investing sacs of the sheath of such young 

 oogonia, protoplasmic streaming can be very beautifully seen. 

 The chlorophyll grains have already elongated and taken on a 

 brown tone. In subsequent stages the oogonium becomes oval, 

 and the central cell, the egg-cell or oosphere, becomes filled with 

 oil-drops and starch grains (Fig. 112) becoming thus opaque ; the 

 starch grains show a beautiful concentric lamination. The in- 

 vesting sheath becomes darker, and masses of lime become 

 deposited on its outer surface. 



Fertilisation. The egg-cell is receptive, i.e., is ready for 

 fertilisation, at the same time when the antheridium of the same 



