F. E. Frit sc It. 
218 
genus Sphaerozyga. 1 The latter was at one time regarded as a 
distinct genus, but since it has been shown that both kinds of spore- 
formation occasionally occur in the same species, its generic position 
has been abandoned. From what is known, it would appear that 
the kind of spore-formation,—whether centripetal or centrifugal,— 
is in some way correlated with external conditions; these must, 
however, primarily exert an influence on the heterocysts, since it is 
in relation to these latter, that the alteration in the phenomenon 
depends. All this suggests, that the heterocyst plays an important 
part in spore-formation, and a consideration of the genus Rivularici 
will force us to the same conclusion. 2 
Although the mature spores are certainly capable of passing 
through a long resting period, in the material, which I investi¬ 
gated, germination can evidently take place very soon after 
their maturation. If filaments containing fully-developed spores 
are placed under unfavourable conditions ( e.g . gradual dessication), 
the vegetative cells become paler and paler and die off, whilst the 
spores loose the granular appearance of their contents and these 
latter become homogeneous and highly refractive. Such' spores are 
evidently in the resting condition and are capable of germination, as 
soon as favourable conditions are restored. These cells are therefore 
scarcely spores (Dauerzellen) in the physiological sense, which 
Brand applies to them, 3 according to whom spores are distinguished 
from gonidia amongst other points by the resting-period, through 
which they pass, and I shall have occasion in a moment to refer to 
other features, which show that the morphological and physiological 
distinction of spore and conidium is not always a sharp one. 
The germination of the spores was observed in situ in the 
thread and a very large number of cases was examined. Consi¬ 
derable variation occurs in the mode of germination, but it in all 
cases leads to the formation of a young thread, possessing all the 
characters of the Anabaena; in one case only, which I have 
unfortunately omitted to figure, did the contents of the spores seem 
to have germinated and divided along two planes, somewhat after 
1 cf. Palla, Beitr. z. Kenntn. des Baues des Cyanophyceen-Proto- 
plasts, Pringsh. Jahrb., Vol. 25, 1893, p. 545; also Schmidle, 
zur Entwickelung von Sphaerozyga oscillarioides (Bory) Kiitz. 
Ber. Deutsch Bot. Gesellsch. Vol. xiv., 1896, p. 393 ; see also 
Fritsch, Studies on Cyanophyceae, No. 1. — New Phytologist, 
Vol. III., No. 4, p. 94. 
2 This will probably form the subject of the next article of this 
series. I have commented on the possible functions of the 
heterocysts in relation to spore-development in the first of the 
studies (see especially p. 93, loc. cit). 
* Brand, Morpholog.-physiol, Betrachtungen, etc., loc. cit., p. 45. 
