206 Chlorophycece 



green stratum on the damp surfaces of calcareous rocks. Diarn. of veg. cells 

 4 12 fji ; zoogonidangia up to 30 p. in diameter ; zoogonidia 1 2'5 /u. in breadth 

 and 3 5 p, in length ; fig. 83 D. Chodat has observed 'fformotila stages' of 

 a species of Pleurococcus, and he also suggests that they may be in part Dacty- 

 lothece Braunii Lagerh., but with this latter suggestion I cannot agree. 



Genus Urococcus Klitz., 1849. The cells are much as in 

 Hormotila Borzi, but are usually of a larger size and their contents 

 are coloured with a red-brown pigment. The cell-wall is thick 

 and lamellose, generally with a considerable increase in thickness 

 on one side. There is frequently an exuviation of the outer layers 

 of the cell-wall. 



The genus is usually attributed to Hassall, but this is due to a 

 misconception. Hassall, in describing the characters of his " First 

 Subgenus" of Hcematococcus Ag., stated 1 that "the term Ouracoccus 

 might be applied to the species of this subgenus." This suggestion 

 was improved upon by Kiitzing, who established the genus 

 Urococcus of Hassall ; but, if Urococcus is to remain as a genus, it 

 must be as " Urococcus Kiitz. 2 " 



U. insignis (Hass.) Kiitz. [ = Hcematococcus insignis Hass. ; Chroococcus 

 macrococcus Rabenh.] is not uncommon in the bogs of moorland and upland 

 districts. Diam. of cells without integument 25 51 p, with integument 

 41 78 p.. It sometimes occurs in quantity amongst submerged Sphagnum, 

 especially in peaty pools. 



Family 6. HYDRODICTYACEJE. 



In this family of the Protococcoidese the plant-body consists of 

 a non-motile coenobium of ccenocytes which floats freely in the 

 water. The coenocytes are arranged either as a flat plate or after 

 the manner of a net, and they are of very variable form. In 

 Euastropsis there are only two cells (coenocytes?) in the coenobium, 

 in Pediastrum there may be more than fifty ccenocytes, and in 

 Hydrodictyon there are often many hundreds, the coenobium 

 reaching a length of several centimetres. 



Multiplication sometimes occurs by the formation of autocolonies. 



Reproduction takes place by the development of hypnospores 

 (usually aplanospores), by the formation of new coenobia by the 

 apposition of biciliated zoogonidia which have become quiescent, 

 and in some by the fusion of isogamous gametes to form a zygo- 

 spore. The germination of the zygospore is indirect. 



1 Hassall, Brit. Freshvv. Alg. 1845, i, p. 322. 



2 Kiitzing, Spec. Algar. 1849, p. 206. Vide West & G. S. West in Journ. Bot. 

 June, 1897, p. 239. 



