190 CHAETOPHORACEAE 
conjugation of the large and small gametes of the former to the 
oögamous fertilization of the latter. 
Lem 
MICROTHAMNION Nägeli; Kütz. Spec. Alg. 352. 1849.‏ ۔ 
Kirchn. Krypt. Flor. Schles. 2': 70. 1878.  Borzi, Nuova.‏ 
Notarisia, 2: 390. 1891. Schmidle, Hedwigia, 38: 165-170.‏ 
.1899 
Thallus minute, attached by a bulbous basal cell, much 
branched. Branches throughout of about the same diameter as 
the main stem. In the formation of a branch, a growth is pushed 
out at the upper end of a cell and the wall of separation is formed, 
not at this point, but some distance above in the branch. Cells 
cylindrical, the cell-wall very thin. Chromatophore a thin sheet, 
more or less completely covering the cell-wall, without pyrenoids 
but containing oil-drops. 
Asexual reproduction through zoóspores formed in any cell 
(the basal excepted) to the number of 4 or 8 ; they are ovoid in 
shape, biciliate, without eye-spot, and germinate (apparently) 
directly after adhering to a substratum, without rhizoid formation. 
. Inhabitants of fresh water. Type M. Kuetzingianum Nag. 
[ Etym. نمم‎ small, and Hapvior, a little bush.] 
This genus has frequently been placed in close relation to 
Trentepohlia (e. g., by Wille in Die natürlichen Pflanzenfamilien), 
because it has been supposed to have special terminal sporangia. 
In all the forms, however, with which we are familiar, any cell in 
the plant may produce zoóspores, and with less swelling of the 
filaments than in most of the Chaetophoreae. We have often 
seen many of the lower cells of a branch hyaline from the loss of 
the zoóspores, before they have escaped from the terminal cells. 
Hence the genus must occupy a position near to Myxonema. The 
remark of Chodat ('o2) * Borzi pretend avoir vu les zoöspores 
biciliées (4-6 2)” is unnecessarily discourteous, as there was every 
reason to expect that zoóspores would be found in these plants. 
Equally unjustifiable is his placing this genus in the Pleurococ- 
caceae. 
Synopsis of Species 
Ramification dense, without distinction between main stem and — 
. Kuetzingianum. 
Ramification more open, erect, the main stem distinguishable to elem summit. 
Terminal cells not narrowed. 2. M. strictissimum. 
Terminal cells slightly tapering. 2b. M. strictissimum macrocystis. 
