PROTOCOCCACE2E. 39 



Ophiocytium, " Science Gossip," June, 1867, p. 127, fig. 103. 

 In pools, mixed with other alga?. 



Plate XIV. fig. 2. a, young cells ; c, older cells ; b, mature cell X 

 400. 



GENUS 28. SCIADIUM. Braun. (1855.) 

 Plant from a single individual producing a family. Thallus 

 (solitary) adnate, unicellular ; cell elongated, cylindrical, 

 straight, attenuated at the base into a slender stem. Gonidia 

 about 8, resulting from division of the cell-contents, at length 

 protruding from the ruptured apex, retained at the mouth and 

 extending in the form of an umbel, each individual becoming 

 developed into a cylindrical cell like the mother-cell. This pro- 

 cess is repeated to a third, or sometimes a fourth generation, 

 forming a composite or decomposite umbel. Ultimate cells 

 producing free biciliate zoogonidia. 



The cylindrical cell of Sciadium possesses uniformly distributed green 

 contents, which are interrupted, iu perfectly developed cells, by light 

 cross streaks, and are divided into a row of 5 to 8 about equal masses, 

 which become gonidia. I could not detect nuclei in the individual seg- 

 ments of the contents passing into the formation of gonidia. Braun 

 Rejuvenescence, p. 260. 



Sciadium arbuscula. Braun Unicell. Alg. p. 106, t. 4. 



Umbellate. Cells straight (rarely falcate), obtuse at the apex ; 

 stem about as long as the diameter of the cells. 



SIZE. Cells -0038 mm. (rarely -007 mm.) diam. 



Sciadium arbitscula, Micr. Journ., 1866, p. 4. Archer, Micr. 

 Jonrn. xii., 1872, p. 314. 



Opliiocytiwn arbuscula (Br.), Rabh. Alg. Eur. iii. 68, 



Attached to confervoid alga3 and aquatic plants. 



Braun, writing of this species, says " It displays an originally obovate 

 tube, generally becoming elongated into a cylindrical form, obtuse 

 above, and prolonged into a slender attached pedicel below. The con- 

 tents consist of uniformly green mucilage, in which a small vesicle 

 may sometimes be distinguished, but only in the earliest stage of growth. 

 The pedicel is transparent and colourless, and secretes at its base an 

 originally yellowish brown, afterwards dark brown mass, which gradually 

 expands into a disc-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 open 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 individuals 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 



