<37 
Classification of Gi'een Algce. 
3. Lctterstcdtia. Areschoug, 1850. 
l halius of the same structure as in Ulva, but growing 
out pinnately into numerous membranous lateral 
lobes of limited growth. Sporangia only occurring 
on the lateral lobes which are shed when old. 
4. Enteromorplia . Harvey, 1849. 
Thallus a regula: or irregular, large or small, branched 
or unbranched tube, usually floating freely when adult. 
Cells in one layer, arranged with slight regularity, 
embryonic form a two-layered membrane which 
splits to form the tube; the embryonic form is some 
times persistent at the growing apex. 
5. Ilea . J. G. Agardh, 1883. 
Thallus similar to that of Entevomorpha , but unbranched 
and always attached, usually of a brownish colour. 
Cells arranged in very regular lines. 
Series IV. Ulotrichales. 
Thallus of uninucleate cells, consisting typically of branched or 
unbranched uniseriate filaments. Reproduction by zoospores, by 
isogamous or oogamous gametes, and by aplanospores and akinetes. 
Fam. I. Ulotrichace/e 
Thallus consisting of a single unbranclied cell-thread, fixed to the 
substratum by a (usually) specialised basal cell. Chromatophore a 
single parietal plate. 
Reproduction by 4- or 2-flagellate zoospores, and by 2 -flagellate 
isogametes ; also by aplanospores and akinetes. 
Genera. 
1. Ulothrix. Kiitzing, 1833. 
Cells all equivalent with the exception of the specialised 
fixing cell. Chromatophore parietal, flat, incompletely 
lining the longitudinal wall, and containing one or 
more pyrenoids. Reproduction by zoospores with 4 
or 2 flagella, and by biflagellate isogametes. Geimin- 
ation of zygote indirect. Aquatic forms. 
2. Hormidium. Kiitzing, 1843. 
Specialised fixing-cell absent. Chromatophore as in 
Ulothrix. Multiplication by fragmentation ol the 
thallus into short lengths or into single cells. Repro¬ 
duction also by akinetes, and by biflagellate zoospores. 
Gametes unknown. Aerial forms. 
3. Uronema. Lagerheim, 1887. 
Thallus fixed by a hemispherical basal disc. Chroma¬ 
tophore parietal with uneven margin, containing 
(usually) two pyrenoids. Reproduction by 4-flagellate 
zoospores and aplanospores. Gametes unknown. 
