1913] YAMANOUCHI—ZANARDINIA 19 
of the gamete-producing form, although their similarity might 
mislead those who observe only the external features. 
Formation of zoosporangia 
Zoosporangia are produced on the upper surface of the thallus. 
In the mature plants, the groups of zoosporangia are distinguished 
by patches of darker 
color which contrast 
sharply with the 
light-brown color of 
the sterile portion. 
These patches are 
composed of thou- 
sands of zoosporan- 
gia, produced side by 
side upon the thallus. 
The patches look 
darker than the rest 
because the sporan- 
gia, no matter what 
their age, contain a 
great number of plas- 
tids which have an 
olive-brown color. Fic. 16.—Gametes sketched from living material: 
Tis prodqstiemal GU Page fet er 5 tn ee 
zoosporangia begins female gamete; e and f, 2-celled sporelings from ferti- 
at a certain spot and _ lized gamete; in the sporelings large pigment spots 
proceeds centrifugal- are derived from the female gamete and small ones 
] from the male gamete, 
y,so that the younger 
Stages are generally found at the edge of the patches. The details 
of the origin of the zoosporangium are as follows: A superficial cell 
of the thallus begins to swell, elongates slightly and divides, giving 
rise to two cells, the upper one a zoosporangium initial or zoospore 
mother cell and the lower one a stalk cell (fig. 20, a). The process 
Occurs simultaneously or successively in a number of neighboring 
superficial cells, so that finally zoospore mother cells are produced 
in great numbers, crowded closely together. When the superficial 

