SMITH : TETRADESMUS, A NEW COENOBIC ALGA 85 
mature colony, and then by the liberation of the young colony 
from the mother wall. 
Another similarity between the young daughter cells in Tetra- 
desmus and the swarm spores in Hydrodictyon is in the behavior 
of the pyrenoid. In Hydrodictyon, Timberlake (16) noted that 
after the swarm spores are formed by cytoplasmic cleavage, new 
pyrenoids appear as small red-staining bodies closely associated 
with the nuclei. This is exactly what takes place in Tetradesmus 
and gives us a further basis for considering the young daughter 
cells of Tetradesmus the morphological equivalents of the swarm 
spores of Hydrodictyon. As in Hydrodictyon also, the daughter 
cells at first have no cell wall, but a cellulose wall is formed after 
the daughter cells have settled down into the position which | 
they will have in the adult colony. 
SUMMARY 
1. Tetradesmus is a distinct genus, and not a cultural form of 
Scenedesmus. 
2. Reproduction takes place by the formation of non-motile 
cells (spores) by successive nuclear and cell divisions. These 
spores then become arranged in the form of the adult colony while 
they are still inside the old cell wall. The young colonies are 
liberated by the rupture of the mother cell wall. 
3. The pyrenoids in the daughter cells a arise de novo and not by 
the division of a preéxisting pyrenoid.. 
UNIVERSITY OF WISCONSIN. 
BIBLIOGRAPHY 
. Beyerinck, M. W. Culturversuche mit Zoochlorellen, Lichen- 
gonidien und anderen niederen Algen. Bot. Zeit. 48: 725. 1890. 
. Beyerinck, M. W. Notiz iiber Pleurococcus vulgaris. Centralbl. 
Bakt., Zweite Abt. 4: 785. 1898. 
Chodat, R. Etude critique et expérimentale sur le polymorphisme 
Mémoire publié a l'occasion du jubilé de |’Univer- 
La 
tv 
> 
des algues. 
sité de Genéve. 1909. 
Chodat, R., & Malinesco, O. Sur le polymorphisme de Scenedes- 
mus acutus Meyen. Bull. Herb. Boiss. 1: 184. 1893. 
Chodat, R., & Malinesco, O. Sur le polymorphisme du Raphidium 
Braunii et du Scenedesmus caudatus Corda. Bull. Herb. Boiss. 
I: 640. 1893. 
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