Studies on the Chloroplasts of Destnids. III. 
X. The Chloroplasts of Cosmarium. 
BY 
NELLIE CARTER, D.Sc. 
With Plates X-XIII and two Figures in the Text. 
ERTAIN types of chloroplast structure have long been known to occur 
v__y in the genus Cosmarium. A very common form, especially amongst 
the smaller species of the genus, in which there is a simple four-lobed 
chloroplast with a single central pyrenoid, was described and figured by 
Nageli (1849) and de Bary (1858), as well as certain later investigators. 
In a second type, first figured by Nageli (1849) for C. margaritiferu m 
and C. Botrytis , and later by de Bary (1858), Delponte (1873), and others, 
there are two chloroplasts in each semi-cell, each with a central pyrenoid 
and several radiating plates. 
Lastly, several species of the genus were known to possess parietal 
chloroplasts. De Bary (1858) and Delponte (1873) figured such parietal 
chloroplasts in C. turgidum , whilst the latter investigator also indicated 
a similar condition in C. ovale. Klebs (1879) and Gay (1884) also figured 
parietal chloroplasts in C. de Baryi and C cucumis respectively, and 
Ltitkemuller (1893) investigated the more detailed structure of some of 
these parietal chloroplasts. 
Chloroplasts of all these types were figured in many species by W. and 
G. S. West (1904-11), and in this work it is also indicated that other types 
of structure than these three probably occur in the genus, but without care- 
fully stained material it is impossible in most cases to determine the 
structure of the chloroplasts, and in the majority of species definite 
information is entirely wanting. 
It has long been known that the majority of the genus have axile 
chloroplasts, and several investigators have considered the comparatively 
few species known to possess parietal chloroplasts to be worthy of a special 
genus. Thus Lundell (1871) instituted the sub-genus Pleurotaeniopsis to 
contain all such species, and Lagerheim (1887) raised this to the rank of 
a genus. Again, Gay (1884) created a new genus Cosmaridium to include 
[Annals of Botany, Vol. XXXIV. No. CXXXIV. April, 1920.] 
