182 PHYLUM III. ZYGOPHYCEAE 
Microspora and Ulothrix could very well serve as the 
originals which have been modified successively into 
the Pond Scums, the Desmids and the Diatoms. The 
limited fragmentation of the filament in Ulothrix is so 
much increased in the Conjugate Algae as to render the 
production of zoospores unnecessary. In like ‘manner 
the sluggish protoplasm of the Conjugate Algae is corre- 
lated with the disappearance of the freely motile gametes 
and the degeneration of the sexual process into a sluggish 
conjugation, which in some Desmids and Diatoms results 
in the partial (if not complete) suppression of the sexual 
act. According to this view ‘‘conjugation”’ is the result 
of degeneration. It is sexual reproduction on its way 
toward disappearance. Instead of affording an example 
of the beginning of sexuality, as has so often been sug- 
gested, these plants show sexuality on its way to disap- 
pearance. Furthermore, it is obvious that the Conjugate 
Algae constitute a lateral phylum which is related to 
other phyla only in its lower members, and that its higher 
members depart more and more widely from all other 
forms of plants. ° | 
Laboratory Studies. (a) Collect a quantity of bright green 
pond scum, which always abounds in shallow ponds and pools in 
the spring, summer and autumn, and preserve in a dish of 
water. Collect, also, some which has begun to turn yellow and 
brown. Upon mounting a little of the first in water and exam- 
ining with a high power it will be found to consist of threads 
of cylindrical cells, each containing one or more spiral chloro- 
plasts (Spirogyra) or star-shaped chloroplasts (Zygnema). 
Upon mounting some of the second collection, here and there 
the formation of resting spores may be observed. In all cases 
care must be taken not to mount too great a quantity of the 
material, nor to injure the plants by rough handling. 
(d) Collect a quantity of pond scum and other aquatic 
vegetation. Mount portions of this material and search for 
desmids, using a low power objective. Two-lobed desmids 
