190 



Tetrasporinede 



or by the formation of a tetrad of four .daughter-cells within the wall 

 of the mother-cell, which then becomes mucilaginous. In Palmodictyon 

 hypnospores with brown cell-walls are formed (G. S. W., '04), and after a 

 period of rest these germinate directly into new elongated colonies. 



The genera are : Glceocystis Nageli, 1849 [in part] ; Palmodictyon Kiitzing, 1845 ; 

 Hormotila Borzi, 1883 ; Asterococcus Scherffel, 1908. [Inoderma Kutzing is very doubtful.] 



It has been asserted by various recent authors (Gerneck, '07 ; Wille '09 ; etc.) that 

 Nageli's genus Glceocystis merely includes developmental stages of members of the Chlamy- 

 domonadeEe and Ulotrichales, and should therefore be deleted. This is very likely true of 

 a number of the so-called species which were at one time described, but there is as yet no 

 proof that this is so in other cases. In Glceocystis gigas, for example, the colonies appear 

 to be quite distinctive, and four daughter-cells arranged from the first as a tetrad are 

 usually formed in each mother-cell. Much further investigation is required on some of 

 these Algse. 



Family Dictyosphaeriaceae. 



This family is closely allied to the Palmellaceae, but is easily distinguished 

 by the fact that portions of the old mother-cell-walls remain as thong-like 

 attachments to the cells and cell-groups. This character is best seen in 

 Dictyosphierium, in which the persistent portion of the mother-cell-wall 



ZW 



Fig. 116. Dictyosphserium pulchellum Wood. 1, old colony ; 2, single cell dividing ; 3 and 4, 

 two views of group of four cells, g, mucilaginous envelope ; zw, cruciform remnants of 

 old cell-wall connecting the daughter-cells. (After Senn, from Oltmanns.) x about 1000. 



may become either a bifurcate or quadrifurcate thong (fig. 116) playing a 

 considerable part in maintaining the definite globose or ellipsoid form of 

 the colonies, which are in addition enveloped in a copious mucilage. In 

 Radiococcus the relics of the mother-cell-walls are less important as binding- 

 strands, possibly on account of the fact that the colonies are attached by 

 one side of the large mucous envelope to the leaves of aquatic macrophytes, 

 whereas those of Dictyofphseriwn are free-floating. In Westella and 



