80 SmiTH: TETRADESMUS, A NEW COENOBIC ALGA 
in any except the old, yellow-colored cultures. The ‘‘stroma’”’ 
starch is also produced in much larger quantities in the Scene- 
desmus cell than it is in the Tetradesmus cell. 
The nucleus is usually at the inner side of the cell (FIG. 1), but 
it as well as the pyrenoid may lie in the long axis of the cell (FIG. 2). 
Frequently the nucleus and the pyrenoid are symmetrically placed 
in the long axis of the cell. There is always a single nucleole 
within the nucleus. The chromatin seems to have a very fine 
granular structure, and the only apparent difference between the 
cytoplasm and the non-nucleolar part of the nucleus is the greater 
density of the latter when the material is stained with Heiden- 
hain’s iron-alum-hematoxylin. 
REPRODUCTION 
Reproduction always takes place by the formation of auto- 
colonies within the mother cell wall. The formation of zoospores 
or motile gametes was never observed. In this respect the form 
resembles Scenedesmus, whose sexual reproduction is unknown. 
The division of the nucleus was not observed with certainty, 
on account of the minuteness of the nucleus, but stages in the 
cleavage of the cell were found in sufficient abundance to warrant 
the assumption that the following is the correct description of the 
process. 
The nucleus divides so that the daughter nuclei lie in a line 
parallel to the long axis of the cell, as shown by a cell containing 
two daughter nuclei (FIG. 9). This stage was found in great 
abundance, and the two daughter nuclei were always found at 
the inner side of the cell. Following this division of the nucleus 
comes a cleavage of the cytoplasm, so that each half of the 
protoplasmic mass contains a nucleus (FIG. 104 and 10B). This 
division takes place by the formation of a cleavage furrow from 
the outside toward the center. The process seems to be similar 
to that observed by Harper (7) in the spore formation of certain 
fungi and by Timberlake (16) in the swarm spore formation of 
Hydrodictyon. The daughter cells resulting from this division are 
two naked protoplasts which lie close to one another and are not 
separated by a wall. The pyrenoid does not divide during this 
process; consequently, at the end of the first cleavage one daughter 
