VARIATION IN THE DESMIDIEX. 399 
III.— Variations of Cell-contents. 
The arrangement of the chromatophores and the included 
pyrenoids is frequently a conspicuous feature of living Desmids, 
and it may be truly said that some particular disposition of these 
structures is one of the most constant features exhibited by 
several large series of these plants. Taking this into considera- 
tion, Lundell*, and also Boldtt, described several subgenera of 
Desmids founded mainly on the structure and disposition of the 
chromatophores. Subsequent observers elevated some of these 
subgenera to the rank of genera (e. g. Pleuroteniopsist and 
Pleurenterium§); and the arrangement of the chromatophores 
thus assumed an important place in the study of this family of 
Alge. 
Moreover, the genus Cosmaridium was founded by F. Gay || 
on precisely those characters which were utilized by Lundell for 
Pleuroteniopsis, his subgenus of Cosmarium, viz. :—“ Chromato- 
phori e teniis parietalibus, margine irregulariter lobata, pyren. 
nonnulos involventibus formati." 
There are many strong reasons against the utilization of such 
easily destructible characters for generic distinctions, chief among 
which is the fact that living plants alone could be correctly 
referred to their true genera. Death so far renders the nature 
of the cell-contents undeterminable that were certain genera 
of this kind authoritatively recognized, specimens sent from 
abroad—and such specimens are generally dried or enclosed in 
preservative media—could not be satisfactorily referred to their 
proper systematic position; moreover, before these characters can 
be utilized positive proof of their importance has to be obtained, 
and how can this be done better than by a study of their 
variation ? 
A short paper by Lütkemüller| is the only contribution I can 
* P. M. Lundell, “ Desm. Suec.,” Act. Soc. Scient. Upsal. 1870. 
t R. Boldt, *Desm. fran Grönland,” Bih. till K. Sv. Vet.-Akad. Handl. 
Bd. xiii. Afd. iii. no. 5, 1888, p. 31. 
+ Utilized as a generic name by G. von Lagerheim in ‘ Botaniska Notiser,’ 
1887, p. 197. 
$ Elevated to a genus by N. Wille in Engler and Prantl, “Die Naturl. 
Pflanzenfam.’ 1890, p. 11. 
| F. Gay, “ Note sur les Conj. du Midi de la France,” Bull. Soc. Bot. France, 
tom. xxxi. 1884, p. 340. 
€ J. Lütkemüller, ** Beobacht. über die Chlorophyllkórper einig. Desmid.," 
Oesterr. botan. Zeitschrift, xliii. 1893, no. 1, pp. 5-11, no. 2, pp. 41-44, tt. 2-3. 
