i to Chodat . — On the Polymorphism of the Green 
cell twice transversely ; the four superposed cells show 
a tendency to elongate and to assume the spindle form of the 
mother-cell. Finally, by absorption of the cell-wall they are 
set free, as though they had originated by simple fission. 
When there are some filaments of Vaucheria or other Algae 
in a culture of Raphidium Braunii , the latter plants develop 
a little disk at one end by which they become attached to the 
filament. In this case the difference between the two poles 
is clearly demonstrated by the behaviour of the products of 
division. In most of the individuals so attached, the wall 
of the mother-cell becomes more resistent at the base, and 
only the upper part is dissolved ; the new Raphidia are 
discharged and very often remain attached to the edge of the 
cupule-like mother-cell. This process being repeated, a very 
elegant bush-like colony arises, and a certain similarity to the 
case of Sciadim/i is produced. 
The polymorphism of this species is very considerable. 
A similar evolution of the fixed stage of Dictyosphaerinm has 
also been described after repeated observations. 
All these different Protococcoideae can be reduced to uni- 
cellular globular conditions, in which they behave like the 
sporangia of Palmella or Dactytococcus h I have also obtained 
from all the genera a gelatinous condition like Palmella by 
the suppression of the motile element and the disappearance 
of sexual differentiation. Up to the present time isogamy 
has been described in only a very small number of species. 
The Pediastreae constitute only a parallel group or sub- 
order to the former one. 
As I have just shown that the coenobium of Scenedesmus , 
Raphidium and others can be derived from unicellular and 
spore-producing types, the same theory is also applicable to the 
Coenobieae. Leaving aside Hydrodictyon , which seems to be 
a very peculiar type, the others are grouped in several small 
series. 
The first series has as its higher type the curious genus 
1 Chodat, Bull. Herb. Boiss., 1895. 
