Studies on Cyanophyceae. 225 
■opened laterally (very rarely terminally) and had protuded the 
contents as a spherical gonidium with a well-marked wall, which 
were then found lying on one side of the empty mother-cell' (Figs. 
27 and 28). Frequently the wall of the latter becomes distinctly 
mucilaginous (Fig. 29) and, in these cases, the contents are 
probably not protuded at all. The contents were never observed 
to have divided before liberation, and even in the liberated ones 
this was a rare phenomenon. I think it probable that the liberated 
gonidium is capable of passing through a resting-period. 
If we carefully compare the gonidia-formation with the spore- 
formation of Anabaena we find one marked point of difference ; the 
gonidia are surrounded by a definite wall at an early stage. Brand’s 
Fig. 15 (loc. cit.) of Ph'ormidium uncinatum also shows this point 
(cf. also his Fig. 17), although the fact is not directly stated in the 
text. In the case described by Brand, the gonidia are quite 
evidently formed by a contraction (and rounding off) of the cell- 
contents and in Anabaena there is also some contraction, although 
it is not so marked as in Phormidium. On the other hand, the way 
in which the gonidia of Anabaena are liberated quite recalls the 
liberation of the contents of the spores, the membrane, enclosing 
the liberated cell, being either broken open on one side or becoming 
entirely mucilaginous. The main difference therefore lies in the 
fact that the gonidium has a well-marked wall at an early stage, 
whereas in the case of the spores this is as a rule not recognisable 
until some time after the liberation of the contents. Brand sum¬ 
marises the differences between spore and gonidium, as follows :— 
Sowohl inbezug auf die Entstehung als auf die schliessliche 
Entwicklung ware ein vollstiindiger Gegensatz zwischen Dauer- 
zellen and Gonidien gegeben, indem erstere ohne Zellverjiingung 
entstehen und erst nach einer Ruhezeit bei der Keimung Vollzell- 
bildung oder vielleicht auch Vielzellbildung eingehen, wahrend die 
uns hier beschaftigenden Gonidien durch Zellverjiingung entstehen, 
dann aber direkt in den vegetativen Zustand iibergehen ” (loc. 
cit. p. 45). The rejuvenescence of the contents is certainly much 
better marked in the gonidia than in the spores, but I am very 
doubtful about the physiological distinction. I have already 
pointed out above that the spores seem capable of germination 
on maturity and the observations I have made on the liberated 
gonidia point to their not as a rule germinating immediately on 
liberation. In fact the gonidia-formation in Anabaena seemed to 
1 No case of gradual profusion of the gonidium was observed, 
comparable to that of the spores, described on p. 219. 
