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OF A STIPITATE FHESHWATER ALGA. 459 



In the earliest stage, the Dictyosphcerium caunot be distin- 

 guished from a small specimen of Fleurococcus vulgaris, Meneg. 

 The cell-wall is at first about 1/* thick, and consists of cellulose, 

 becoming bluish-violet on the application of chlor-iodide of zinc. 

 As the cell increases in size, but before it shows any signs of 

 fission, the cell-wall increases in thickness, and at the same time 

 becomes mucilaginous, with indications of stratification, and in 

 Ibis condition the cellulose reaction is confined to the innermost 

 firm layer, which corresponds to the original cellulose wall, the 

 peripheral mucilaginous laver becoming brown with a solution of 

 iodine, and behaving in many respects more like protoplasm than 

 any modification of cellulose. The chlorophyll is of a very bright 

 ytllow-green, but the presence of cbromatophores was not satis- 

 factorily determined. The application of hematoxylin reveals 

 the presence of a nucleus, especially after the specimen has been 

 treated with absolute alcohol for a few minutes. When the 

 chlorophyllose portion of the spherical cell attains a diameter of 

 about Gp, it divides simultaneously into four equal parts by two 

 septa developed in two planes at right angles to each other. 

 The septa do not extend quite to the centre of the mother-cell ; 

 consequently the four lobes into which it divides remain organi- 

 cally united in the centre by thin portions about 2ft diameter, and 

 may be compared to four plums united by their stalks in the 

 centre of the group. The mucilaginous portion of the mother- 

 cell-wall does not divide along with the chlorophyllose portion, 

 but continues to increase in quantity, and envelops the segments 

 >n a continuous hyaline stratum. After segmentation of the 

 mother-cell the segments, at first more or less angular, become 

 spherical, still remaining attached by their central stalk-like 

 portions, which continue to increase in size until they attain a 

 length of about 10/* ; these stalk-like portions are usually perfectly 

 Mine, with a very minute lumen, which under a high magnifying- 

 powcr is seen to contain granular fragments scattered here and 

 ft ere, which are sometimes coloured green. 



In old plants the stem-like connecting portions have the 

 lu men completely obliterated. By the time the connecting 

 portions have reached the length of about 10 M , the chlorophyllose 

 Portions of their enlarged apices have respectively assumed the 

 appearance and size of the original mother-cell immediately 

 before segmentation ; each swollen apical segment of the cell is 

 now surrounded by its own mucilaginous coat, the whole being 





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