of the Desmidiese and Diatomese. 5 



number of small Closteria, for the most part beginning to divide*. 

 But the certainty which can only be given by direct observation 

 of the development was altogether wanting. 



The development of four daughter-cells in the interior of 

 spores produced by the conjugation of two individuals (with 

 participation of the whole of the cell-membrane), has been de- 

 monstrated by Alex. Braunf for the Palmellacean Palmoglcea 

 mac7'ococca, Kiitz. (?). Closer still than this species, to the diffi- 

 cult-to-be-defined limits between Palmellacese and Desmidiese, 

 stands another form of the same genus, agreeing almost in ex- 

 ternal form with the Penium Jenneri, Ralfs, but one-half smaller ; 

 in form and magnitude like Mesotanium Endlicherianumj Nag. J 

 In particular individuals the chlorophyll of the contents exhi- 

 bited the arrangement described by Nageli as typical for his 

 Mesotcenium, forming a band-shaped body lying in the longitu- 

 dinal axis of the cell, similar to what Alex. Braun has observed 

 in Palmoglcea macrococca^. This form, perhaps P. protuberans, 

 Kiitz., occurred in many thousands of specimens on the surface 

 of water, in a vessel in which other Algae were cultivated. The 

 closely-crowded individuals of Palmoglcea formed a connected 

 green film with a dry upper surface, to which the air strongly 

 adhered. Each cell contained a very distinct nucleus in the 

 centre, the diameter of which amounted to a fourth or a third of 

 that of the cell. In each half of the cell occurred, in elongated 

 cells two, in shorter cells one, globular chlorophyll-mass, con- 

 taining starch (fig. II), The central nucleus vanished before 

 the division of the cell (fig. 12), a new nucleus then making 

 its appearance in each half (fig. 15). The origin of the lateral in 

 the place occupied by the primary nucleus, and the subsequent 

 removal of the halves resulting from division towards the ends 

 of the cell, as occurs in Spirogyra ||, is altogether improbable in 

 this Palmoglcea; for not only were cells (about to divide) tem- 

 porarily devoid of a nucleus met with frequently, but the larger 

 chlorophyll-mass lying in the path of the secondary nuclei would 

 offer an obstacle to its progress scarcely to be overcome. Divi- 



* See 'Verjiingung,' &e. p. 143 (Ray Translation, 1853, p. 134). I 

 have also often seen such cysts, which probably belonged to Closterium 

 aeerosum : in the spring of 1856, also, some which, occurring in company 

 with Penium closterioides, Ralfs, and containing totally uncurved indivi- 

 duals, must be referred to this plant. Closterium aeerosum was not pre- 

 sent in this water. I was not successful in discovering intermediate stages 

 between them and the spores, 



t Al. Braun, Verjiingung, &c. pp. 145, 351. pi. 1. fig. 42 (Ray Translation, 

 1853, pp. 136, 285. pi. 1 & 2). 



X Nageli, Einzell. Algen, p. 109. 



§ Verjungung, p. 350. pi. 1. fig. 11 (Ray Transl. p. 328. pi. 1. fig. 11). 



II Al. Braun, Verjiingung, p. 258 (Ray Translation, p. 240) ; Pringsheim, 

 Bau der Pflanzenzelle. Berlin, 1854, pi. 3. fig. 1 a. 



