Tort] LUTMAN—CLOSTERIUM 425 
the chromosomes do not come morphologically from the nucleolus, 
there is a possibility that part of the material from that body goes 
to form them. 
The relationships of the desmids to the other groups of the 
Conjugatae is a rather puzzling one. While the great majority of 
them are unicellular, the tendency to form filaments appears in 
such genera as Cosmarium, Euastrum, and Staurastrum. BESSEY 
(3) has gone so far as to divide the desmids on this basis into three 
tribes: Desmideae, cells in unbranched filaments: Anthrodieae, 
cells solitary, elongated, but at not all or only moderately 
constricted; Cosmarieae, cells solitary, broad, and deeply con- 
stricted. 
West (46) in studying variation in desmids came to the con- 
clusion that the group is a degenerate one derived from a filamentous 
Conjugate ancestor, probably among the Zygnemaceae. On this 
basis of degeneration ‘he claims to be able to explain many facts 
Previously difficult of interpretation. He holds that this degenera- 
tion has developed the highly specialized morphological characters 
of the different groups, thus explaining their beauty and variety 
of form, and that with it too has gone hand in hand the loss of 
Sexual differentiation of the conjugating cells. LtrKEMULtER (26), 
4S a result of his very careful study of the cell wall of members 
of the different groups of desmids, has arrived at practically identi- 
cal conclusions as to their phylogeny. 
The position of the young transverse wall in Clostertum also 
seems to throw some light on this question of phylogeny. The 
hew cross-wall is put in at right angles to the old walls in a manner 
that is not in any essential different from that of the filamentous 
Conjugatae such as Spirogyra. It is only as the cells separate and 
the pressure is relieved on one side of this wall that the shape 
changes. If the cells should not separate, a filament being formed, 
€ach cell of the filament would not be essentially different from a 
cell of Zygnema with its nucleus at the middle and a half of the 
Symmetrical chromatophore on either side. While the pointed 
Shape which the new end assumes is obviously a secondary and 
acquired character, in the ontogeny of the transverse wall, we would 
seem to have a bit of the phylogeny of Closterium repeated. 
