Olive. Mitotie division of tlie nuclei of tlie Cyanophyceae. 
27 
otliers sav tliat its absence, alono- witli tliat of tlie nuclear mem- 
braue is only proof of tlie primitive nature of tlie cyanopliyceous 
micleiis. Wäger, liowever, says tliat. linder certain conditions, 
tlie cliromatin substance of tlie central body is f'ound Condensed 
into a single deeply stained grannle snspended by delicate fibers 
in tlie center of tlie cell. I liave not seen sucli a structure as 
lie describes in tlie forms wliicli I bave examined, but, in tlie 
resting nuclei of spores and lieterocysts, some of tlie cliromatin 
granules are sometimes larger than otliers and miglit readily 
pass for nucleoli. Many nucleoli among tlie lower plants and 
tlie Protozoa are undoubtedly merely large masses or granules 
of cliromatin; and, if we could produce by experiment resting 
nuclei in tlie vegetative cells of tlie Cyanopliyceae, it is possible 
tliat we would liave also in tliese plants such a concentration 
of cliromatin substance. 
Tlie resting* nuclei in spores and lieterocysts. 
Tlie nuclei of spores and lieterocysts are of special interest 
in tliat tliey furnisli anotlier point of evidence in support of tlie 
conclusion tliat tliere is no wide and unsurmountable difference 
between tlie nuclei of tlie Cyanopliyceae and tliose of liiglier 
plants. It will be seen tliat tlie nuclei in figs. 49 and 91, 
representing young lieterocysts of Calothrix and Cylindrospermum 
respectively; as well as tke nuclei sliown in fig. 58, a spore of 
Xostoc- and in 93, a spore of Cylindrospermum; and especially 
tliose in figs. 100—103, cross sections of young spores of Cylindro¬ 
spermum, resemble closely tlie resting nucleus witli wliicli we 
are familiär. A cavity, in wliicli we see cliromatin granules, 
and a more or less clearly defined, delicate, nuclear membrane, 
now contribute to tlie resemblance, wliicli was lacking in tlie 
vegetative stages. 
Botli He gl er and Ko kl come rigktly to tlie conclusion 
tliat tlie cell contents of lieterocysts become finally disorganized, 
and tliat tlie nucleus, cliromatopliore, cyanopliycin granules, and 
slime globules gradually disappear. In kg. 77 1 wkicli is stained 
witk metliylene blue, eacli of tlie vegetative cells of tlie filament 
of Cylindrospermum sliows one or more slime globules, tlie spore 
one only, wkile tlie young lieterocyst kas two exceedingly 
minute, reddisk slime globules in a bluisk background. Wken 
older, we find in lieterocysts no indication wkatever of any 
granulär contents, except tlie disorganized cliromatin of tlie dead 
nucleus (note tlie lieterocysts of figs. 37, 38, 50, 53, 80. 88). It 
is kigkly important to note, liowever, tliat in tlie young lietero- 
cysts of Calothrix and Cylindrospermum, before disorganization 
occurs, tlie nucleus apparently begins to enter a normal resting 
condition and to form a nuclear vacuole. 
Tlie mature spore of Cylindrospermum sliows one remarkably 
curious feature, wliicli to tlie writer remained for a long time 
an inexplicable puzzle. It will be noted tliat in fig. 77, a lialf 
matured spore of Cylindrospermum , tlie multitude of cyanopliycin 
