A cton. — Observations on the Cytology of the Chroococcaceae. 447 
accumulation of chromatin at the nodal points. In the remainder of the 
protoplast this fine reticulum is disappearing, and a coarser one, characteristic 
of higher plants, is arising. 
This distinction appears to me to be sufficient to warrant the separation 
of the protoplast into ‘ cytoplasm 5 and ‘ nucleus \ Division, although 
it takes place by constriction of the cell, is initiated by the ‘ nucleus This 
divides and separates, and then the constriction in the cell-wall appears 
(Fig. 19). So that there is a physiological differentiation as well as 
a morphological one. 
The ‘nucleus’ is certainly primitive. It divides by constriction, and 
there is no evidence whatever of mitosis (Fig. 18). It seems to permanently 
remain in a condition resembling the resting stage of the nucleus in higher 
types. 
Repeated division of the cell seems to diminish the comparative size of 
the ‘ nucleus ’, for in the older cells the ‘ nucleus ’ is always small. Possibly 
reproduction takes place in some other way, as it seems essential that 
rejuvenescence of the ‘ nucleus ’ must take place sooner or later. No trace 
of fragmentation of the nucleus, as described by Gardner (’06) in Dermo- 
carpa , has been seen in Chroococcns macrococais , although in examining 
living material I have occasionally observed groups of eight daughter-cells 
free within the old cell-wall. 
(c) Systematic Position. 
Though the protoplast of the Alga described above is more highly 
developed than that of other Chroococcaceae, the connexion between them 
is clearly shown, and there is no reason therefore to separate it from 
the group on this account. It is undoubtedly a member of the Cyano- 
phyceae, and agrees in all essentials with Chroococcns macrococcus , Rabenh. 
Hassall (45) describes an Alga under the name of Haematococcus in- 
signis , which he suggests should be placed in a separate genus, f Urococcus\ 
characterized by transversely corrugated prolongations. The cells are 
described as being spherical and blood-red, with numerous vesicles and 
ringed prolongations. It is not unlikely that this Alga is identical with 
Chroococcns macrococcus. It has been shown that the Chr. macrococcus 
is capable of developing a ringed prolongation on being removed from 
a solid medium to a liquid one. The two algae are identical in size, but 
though Chr. macrococcus often contains several large blood-red pigment 
spots, it has never been described as completely blood-red in colour. This 
may possibly result from a prolonged resting condition. 
Kiitzing (’49) refers to Haematococcus insignis as Urococcus insiguis, 
and states that the stalk is short or absent, and the ‘nucleus’ blood-red. 
This is, of course, still more in agreement with Chr. macrococcus . 
