200 
Fritsch, Stiidies on Cyanophyceae. 
living condition, altliongli stains rnake tliem skow up more 
prominently. In yonng stagos tlio nincli smallci size of tlie colls 
makes the determination of details a great difficulty; nor is tke 
inner investment very strongly developed at tkat period and 
consequently it is very difficult to distingnisk between it and a 
possible rndimentary cell-sbeatli. Tke two investments of tke 
protoplast only become skarply defined in well-advanced sporo- 
genous filaments, — a fact, wkick is not surprising, wken we 
consicler, tkat tkeir origin (as an excretion from tke protoplast, 
is tke same. It is natnral to expect tkat tke cell-skeatlr will 
become more dekned, as tke protoplast becomes older, and will 
reacli its most marked differentiation, wken tke spore develops, 
i. e. wken tlie necessity of a firmer outer covering is fnlly 
realised. 
As tke cells of a filament pass over into tke sporogenous 
condition tke transverse limits of tke cell-skeatks of adjacent 
cells become better defined (cf. fig. 5 and 8). Gradnally also 
W tke increase of tke colomless intercellular septum tlie cells 
niove furtlier apart. wkilst tke cell-skeatli increases in extent 
and closes in round tke open ends, so tkat tke outer investment 
ultimatelv for m s a complete skeatk romtd tke inatine spore 
(fig. 6). As tke skeatk closes in it envelopes a portion of tke 
intercellular septum so Tkat tke skeatk or exospore of tke 
spore (fig. 6, ex) surrounds a complete inner Investment or 
endospore (fig* 6* en). Tke remainder of tke intercellulai 
septum kas swollen up considerably and kas become in visible: 
it is tke cause of tke now more or less wide Separation of 
tke spores. Tke spores tkus exliibit two well-marked mem- 
branes, as in tke cases, described by Gfomont and Boi zi. 
Witk regard to tke spores tke former (loc, cit. p. 233) remarks: 
..La spore enfin, la ou eile existe, est bien, comme on badmet 
generalement. produite par l'encystement d'une cellule vegetative. 
Elle possede un exospore ou se retrouvent les enveloppes de 
celle-ci, et un endospore produit au moment de la maturite, et 
identique par ses proprietes a la membrane cellulaire vegetative.’* 
Brand (03, p. 34) also considers tkat „das Endospoi . . . ei.>t 
bei der die Keimung einleitenden Zellverjüngung entstellt. . . . 
nur an ganz reifen Exemplaren vorlianden ist”. Gfomont and 
Brand tkus regard tlie endospore as produced at tke moment 
of maturity; in A-Uübaenci botli tlie envelopes of tke spoie aie 
liowever present long before maturity is reaclied and. if eitliei. 
it is certainly tke exospore in my opinion, wkick is newly 
formed. Tke process is scarcely one wkick comes under tke 
narne encystment. Düring tlie development of tke spores tlie 
cells increase very muck in size and tke fully-developed spore 
is 2—3 tirnes langer tkan tke ordinary vegetative cell; tliere is 
kowever very little ckange in colour 1 ) in tke species. wkick I 
i) The cell-contents are skghtly yellowish-green, bnt conld scarcely he 
called coloured (cf. Brand 03, p. 33). 
