MUL TINUCLEA TM 281 



of the 'single cell, which nowhere else in the vegetable Tiingdom attains 

 anything like so great dimensions. Under ordinary conditions the in- 

 dividual is entirely unseptate, except where it is about to form repro- 

 ductive bodies, whether sexual or non-sexual. The very large number 

 of nuclei is universal in the Siphonocladaceae ; and, although their 

 occurrence in the Siphoneae rests chiefly on the evidence of Schmitz, 

 there can.vbe little doubt that this order also shares in the peculiarity, which 

 does not lead on to cell-division, as in the groups of algae already 

 described ; and this must clearly be regarded as indicative of a lower or 

 more ancestral type of structure. Whether the Siphonocladaceae and 

 Dasycladaceae are an earlier form leading up to the Siphoneae, or 

 whether they have been derived from the latter by retrogression, indi- 

 cated by the suppression of the sexual organs, is uncertain, though the 

 probability appears to be in favour of the latter hypothesis. 



Order i. — Siphoned (Cceloblast^). 



The thallus is in this family ordinarily unicellular, although often 

 copiously branched, until the commencement of the formation of the 

 organs of vegetative propagation or of sexual reproduction. 



In the genus Vaucheria DC, which alone represents this order, the 

 plant consists, when in a non-reproductive state, of a single elongated cell 

 of a pale green colour, branching in various ways, sometimes as much 

 as a foot in length, increasing by apical growth. Maupas (Comptes 

 Rendus, /.f.) and Schmitz (Sitzber. Niederrhein. Gesell., 1879) state 

 that each tube contains a large number of nuclei. The non-sexual 

 organs of propagation are of two kinds, motionless resting- spores and 

 motile zoospores. The former are produced simply by the abstriction of 

 ends of particular branches, which swell up to an oval form, become 

 cut off from the rest of the tube by a septum, contract, and finally 

 develop a new cell-wall within the old one, thus affording an illustration 

 of the formation of a new cell by rejuvenescence. This process takes 

 place especially as a result of injury to the thallus. In some cases 

 the newly-formed spore is set free simply by the absorption of the 

 original cell-wall, and falls off with the remains of the mother-cell still 

 attached to it, germinating after a few days ; or it is thrown out with a 

 jerk, and goes through a period of rest as a hypnospore before germinat- 

 ing. Another method is the swelling up to a considerable size of 

 certain branches, which separate at the base, and put out at once one 

 or more germinating tubes. The zoospores are among the most beauti- 

 ful of those of any class of Algae, being of considerable size, and entirely 

 surrounded by a fringe of fine cilia. In their formation the extremity 



