346 PHARMACEUTICAL BOTANY 
This second type of conjugation is called Jdateral conjugation. 
In this case a protrusion of the cell wall of the filament occurs 
opposite the partition wall of adjacent gametes forming a 
channel of communication between the gametes. Pulsating or 
contractile vacuoles, such as have been described in Amoeba 
appear in the protoplast and upon contraction propel the gamete 
in one cell cavity (supplying gamete) over into the cell cavity of the 
other gamete (receiving gamete). ‘The fusion of these gametes 
results in the formation of a zygospore. 
5. ORDER SIPHONALES (SIPHON ALG&).—This group is char- 
acterized by the peculiarity that the organisms constituting it 
possess protoplasm containing myriads of nuclei within a common 
filament or cell cavity not segmented by cell walls. The term 
cenocyte has been given to such structures which consist of a many- 
nucleated mass of protoplasm surrounded by a cell wall. Some 
of the siphon alge reproduce by zoéspore formation, others by 
conjugation as well as zodspore formation while Vaucheria, the 
‘green felt,” stands out alone in reproducing both by the forma- 
tion of a single compound zoéspore and by the production also of 
oégonia and antheridia with resultant fertilization (see Figs. 245 
(6) and 247). 
The various species of Vaucheria occur in water or moist soil 
where they form dense mats of tubular filaments. Each filament 
is unicellular until the time of reproduction, containing cytoplasm 
in which are imbedded thousands of nuclei as well as numerous 
chloroplasts devoid of pyrenoids, and small drops of oil. At the 
time of asexual reproduction a transverse wall is laid down near 
the tip of the filament cutting off a terminal cell or zodsporangium 
in which a many ciliated compound zoéspore is formed. This 
escapes by a break in the end of the sporangium, swims about for 
a brief time and then germinates, sending out one or more 
Vaucheria filaments. In some species a colorless simple or 
branched rhizoidal cell or organ of attachment is developed by 
the filament where it contacts a solid substance. 
6. ORDER CHARALES (THE STONEWORTS).—FAMILY CHAR- 
ACE&.—The highest group of green algze, possessing forms which 
are differentiated into stem-like and leaf-like structures and 
rhizoids. Examples: Chara and Nitella. 
