SEXUAL REPRODUCTION OF THALLOPHYTES. 3803 
A supposed conjugation has been described by Velten! in 
Chlamydococcus. But according to his observations the 
macrozoospores and not the microzoospores took part in it. 
Rostafinski? accordingly concludes from this and other 
abnormalities which occur in Velten’s account that he had 
mistaken for conjugation the destruction of a cell of Chlamy- 
dococcus by a parasitic monad. 
Pandorina was the plant in which the conjugation of 
zoospores was first described by Pringsheim.? He distin- 
guishes it from Hudorina with which English writers have 
generally identified it. According to him it consists of a 
colony of sixteen zoospores, each of which may give rise to 
new colonies by division. This is the asexual mode of repro- 
duction. The first stages of the sexual condition are very 
similar. But in the final result the new colonies resolve 
themselves into their constituent zoospores which are fre- 
quently eight instead of sixteen in number. ‘They vary in 
size, but though there are zoospores that are comparatively 
large, and some which are small, there are others which 
correspond to every intermediate dimension. Pringsheim 
considers that this difference of size indicates a certain 
amount of sexual differentiation. For usually a small zoo- 
spore (antherozoid) conjugates with a large zoospore (oospore). 
When the zoospores which conjugate are equal in size they 
possess the mean dimensions; these might be regarded, 
therefore, as sexually undifferentiated. The largest sexual 
zoospores never conjugate with one another. 
In Pandorina it must be borne in mind that size ceases to 
be a criterion of difference between the vegetative zoospores 
(macrozoospores) and the sexual (microzoospores). 
The phenomena of conjugation repeat what has already 
been stated in Chlamydomonas. ‘The sexual zoospores, ac- 
cording to Pringsheim, appear to seek out and approach one 
another in pairs. They touch by their transparent anterior 
extremities, blend at these points, and eventually form a 
united body geminate in shape. The double notch, which 
indicates the original distinctness of the two zoospores, 
gradually disappears, and the zygozoospore assumes a 
rounded form which gives no indication of its composite 
origin, except that its anterior extremity has two lateral 
be referred to Protococcus, of which it may now be regarded as the motile 
condition. 
1 «Bot. Zeit.,” 1871, p.383. 
2 Thid., 1871, p. 788. 
3 « Ueber Paarung der Schwarmsporen,” Pringsheim, in ‘ Monatsber. der 
Berliner Akad.? Oktob., 1869. 
VOL. XV.— NEW SER. x 
