438 HARPER— ORGANIZATION, REPRODUCTION 



1912. Griggs, R. F. The Development and Cytology of Rhodochytrium. 

 Bot. Gazette, 53 : 127. 



1912. Harper, R. A. The Structure and Development of the Colony in 



Gonhivi. Trans. Am. Microscop. Soc, Vol. XXXI., No. 2, 65-84, 

 April. 



1913. Harper, R. A. Morphogenesis in Pediastrum. Science, II., 37 : 385, 



March 7. 



1913. Smith, G. M. Tetradcsmus, a New Four-celled Coenobic Alga. Bull. 



Torr. Bot. Club, Vol. XL., pp. 75-87. 



1914. Nitardy, E. Zur Synonomie von Pediastrum. Beth. Bot. Centralbi, 



322: III. 

 1914. Smith, G. M. The Cell-Structure and Colony Formation in Sccnedcs- 



mus. Arch. f. Protistenkunde, Vol. XXXII., 278-297. 

 1914. Smith, G. M. The Organization of the Colony in Certain Four-celled 



Coenobic Algae. Trans. Wis. Acad. Sci. Arts and Letters, Vol. XVII., 



I 165-1220. 

 1916. Harper, R. A. On the Nature of Types in Pediastrum. Mem. N. Y. 



Bot. Garden. 

 1916. Smith, G. M. Cytological Studies in the Protococcales. I. Zoospore 



Formation in Characium Sieboldii. A. Br. Ann. of Bot., Vol. XXX., 



459-466. 

 1916. Smith, G. M. Cytological Studies in the Protococcales. II. Cell 



Structures and Zoospore Formation in Pediastrum Boryanum 



(Turp.) Menegh. Attn, of Bot., Vol. XXX., No. CXIX., July. 



DESCRIPTION OF PLATES. 



The photomicrographs were made for the most part with the Zeiss apo- 

 chromatic objective 8 mm. and the compens. oculars, Nos. 8 and 12. They are 

 all of Pediastrum asperum. 



Plate V. 



Fig. 8. Fairly mature, sixteen-celled colony about ready to form swarm- 

 spores. X about 225. 



Fig. 9. A few cells of a still more mature colony more highly magnified, 

 showing the marked reduction in the size of the intercellular spaces. 

 X about 1,125. 



Fig. id. Cells a and b, showing two cell stages, the first cleavage in the 

 short axis of the mother cell. Cells c, d show at least the beginnings of the 

 four cell stages, the second cleavage plane being in the long axis of the 

 mother cell. In cell e the planes are more irregular. X about 1,125. 



Fig. II. Eight-cell stage, perhaps later, the planes of cleavage still show- 

 ing a marked tendency to intersect at right angles. X about 550. 



Figs. 12 and 13. Cleavage complete and the daughter cells more or less 

 rounded up. The whole mass conforms to the outlines of the four-lobed 

 mother cell and there is little evidence of the rectangular intersection of the 

 cleavage planes. Fig. 12 X about 700; Fig. 13 X about 1,125. 



Fig. 14. Less highly magnified view of a thirty-two-celled colony in all 

 of whose cells cleavage is complete. X about 500. 



Fig. 15. Two young thirty-two-celled daughter colonies and two cells 



