THALLOPHYTES 
37 
Conclusions. The body of Siphonales is coenocytic and usually 
complexly branched and differentiated. Zoospores are formed, which 
sometimes take on the character of the coenocytic body and may be 
regarded as compound zoospores, as in Vaucheria. Sexual repro- 
duction ranges from isogamy to heterogamy, in the latter condition 
extending to the formation of special branches bearing the sex 
organs. Aplanospores or non-motile protected cells are produced 
under conditions unfavorable for vegetative activity, and from all 
spores or resting cells there is a direct development of new filaments. 
A possible connection of Siphonales with Confervales is suggested 
by such partially coenocytic forms as Cladophora and Sphaeroplea, 
but in any event it is to be regarded as a highly specialized group. 
(e) Conjugates 
General character. This is also a very 
distinct group, which is separated by some 
writers from Chlorophyceae on account of 
its peculiar features. It is a fresh-water 
group, the bodies being single cells or simple 
filaments, and characterized by remarkable 
chloroplasts, by the absence of swimming 
spores, and by a peculiar method of sexual re- 
production. The absence of all ciliated cells, 
including both spores and gametes, in an 
aquatic group is remarkable. The following 
families may be used to illustrate the group. 
Desmidiaceae. The desmids are one-celled 
plants that exhibit the greatest possible variety 
of form and are often extremely beautiful. 
The cell is peculiar in being organized into 
two symmetrical halves, often separated by 
a deep constriction which makes the isthmus. 
In each half there is a large, irregular, often 
complex chloroplast and several pyrenoids, 
while in the isthmus connecting the two halves 
the single nucleus is placed. Many of the 
desmids can move about, and they are very 
sensitive to light, taking a position determined 
by. the incident rays. 
102 
FIGS. 101, 102. Clos- 
terium: 101, cell dividing, 
the two nuclei and the wall 
having been formed; 102, the 
plastid in an old "half cell " 
having divided, and the 
nucleus becoming; placed be- 
tween the two plastids. 
After A. FISCHER. 
