REJUVENESCENCE IN NATURE. 187 



I will add to these examples of the setting-free of the 

 cells destined for the Rejuvenescence from their " super- 

 annuated" envelopes, a few very strange examples of 

 normally imperfect release of the germ-cells. I have 

 applied the name Sciadium* to a minute Unicellular 

 Alga, which displays an originally obovate tube, gradually 

 becoming elongated into a cylindrical form, obtuse above, 

 and prolonged into a slender attached pedicle below. 

 The contents consist of uniformly green mucilage, in 

 which a small vesicle may sometimes be distinguished, 

 but only in the earliest stage of growth. The pedicle is 

 transparent and colourless, and secretes at its base an 

 originally yellowish-brown, afterwards dark-brown mass, 

 which gradually expands into a disk-shaped foot. When 

 the growth is completed, the green contents become 

 divided into several masses, developing into a series of 

 5 — 8 germ-cells ; the cell-membrane dehisces, throwing 

 off its summit as a finger-stall shaped cover, but the 

 germ-cells instead of leaving the opened tube, all collect 

 at the point of exit with their inferior, narrower, and 

 somewhat pedicellately elongated ends sticking in the 

 tube. Thus is produced a capitule, and by the advancing 

 growth of the young family, an umbel formed of indi- 

 viduals exactly resembling the parent individual from 

 which they originated. The emptied mother-cell tube 

 remains as the stem and support of the umbellate family, 

 and gradually becomes filled from above downwards with 

 the same yellow and reddish-brown secreted substance, 

 which it exhibits at its own base. The imperfect birth 

 of the germ-cells just described, is repeated at the transi- 

 tion to the third, and mostly even to the fourth gene- 

 ration, so that little arborescent groups are produced, 



* Vide Kiitzing, ' Sp. Alg.,' p. 490, who places this little plant in the 

 neighbourhood of Bryopsis. To me, Ophiocytium, Nag., ('Binz. Alg.,' 

 t. iv, a), seem the nearest allied genus; young specimens completely 

 resemble Characium and Ascidium. The only species. So. Arbmcula, occurs 

 near Freiburg on various filiform Alg8e, especially on (Edogonium Lands- 

 boroughii and Vaucheria raeemosa, in the water reservoirs of the Botanic 

 garden. 



