DesmMiacedB 



365 



doubt that the axile chloroplast was the primitive one in Desmids as a whole 

 and that the parietal condition has been acquired by a few scattered species 

 in various genera 1 . In Desmids in which the cell is deeply lobed or incised 

 the form of the chloroplasts frequently follows the external configuration of 

 the cell. 



Pyrenoids are present in the chloroplasts of all Desmids. In most species 

 there are one or two pyrenoids in each semicell, but in the large flattened forms 



Fig. 229. Desmids showing chloroplasts. A, Closterium Ehrenberyli Menegh., x 184. B, Cl. 

 Lcibleinii Kiitz. , x 334. C, Micrasterias oscitans Kalfs var. mucronata (Dixon) Wille, x 184. 

 D, Cosmarium cucurlitinum (Biss.) Liitkein., x 435. E, Staurastrum punctulatum Br^b. var. 

 Kjellmani Wille, x 435. F, Cosmarium subtumidum Nordst. var. Klebsii (Gutw.) W. & G. S. 

 West, x 435. /, front view of cell ; s, side view ; v, vertical or end view. 



of Euastrum (fig. 220 A) and Micrasterias (fig. 223), and in the elongated cells 

 of Closterium (fig. 229 A and B; fig, 231 AD), Pleurottenium, Tetmemorus, 



1 All attempts to split up the genera Cosmarium, Staurastrum and Xanthidium on the basis of 

 axile and parietal chloroplasts have merely resulted in confusion. Such divisions are purely 

 artificial, resulting in the association of species which have no near relationship with each other. 

 In those few species with a tendency to the parietal disposition of chloroplasts it is by no means 

 uncommon to find axile chloroplasts in one semicell and parietal chloroplasts in the other 

 semicell of the same individual. 



