Smith.—Cytological Studies in the Protococcales . III. 463 
definitely established, it was noted that at times the zoospores germinated 
within the old mother-cell wall and appeared like autospores. Search was 
made for zoospores in T. minimum with the possibility in mind that what we 
have been calling normal autospores are really abnormal germinations of 
zoospores into vegetative cells within the old mother-cell wall. Very careful 
observations were made in the hours preceding and following daybreak, 
because it is at those times that zoospores are generally liberated in the 
algae. Since they were not found it seems reasonable to assume that the 
alga reproduces by autospores and not zoospores, but the possibility of 
zoospore formation in Tetraedron is not absolutely excluded, since a normal 
environment can never be produced in a laboratory culture. 
The formation of four, sixteen, and thirty-two autospores by a single 
cell was also observed. Theoretically the formation of two autospores, or of 
a multiple of two higher than thirty-two, is possible, but they were not found. 
In the formation of four autospores the cleavage occurs at the binucleate 
stage of development (Fig. 19), and then a further cleavage divides the cell 
contents into four protoplasts. Sixteen autospores are formed when there 
are eight nuclei in the cell before cleavage. The noteworthy fact in the 
primary cleavage of such cells is that the number of nuclei in the two 
daughter-cells is always equal (Fig. 31). In these cells also a nuclear 
division takes place some time after the formation of the primary cleavage 
plane (Figs. 32, 33), while the pyrenoid disappears at the same time. The 
final product of cleavage is a mass of sixteen uninucleate protoplasts (Figs. 
34, 35). These are more irregularly arranged than when eight autospores 
are formed, so that their derivation is harder to follow. The formation of 
the autospores from these protoplasts takes place as described above. This 
variation in the number of autospores, as previously stated, rests upon the 
nutrition of the mother-cell. 
Summary. 
Young cells of Tetraedron minimum contain a single nucleus and 
pyrenoid. Repeated simultaneous karyokineses may produce as many as 
eight nuclei within a single cell. Autospores are formed by progressive 
cleavage, the number of nuclei increasing during the process. 4, 8, 16, or 
32 uninucleate protoplasts are the final product of this cleavage, these 
protoplasts being metamorphosed over into autospores. The pyrenoid 
disappears after the first cleavage, new pyrenoids being formed de novo in 
the young autospores. 
