BATRACHOSPERMUM. 55 



BANGIA ATRO-PURPUREA, (Dillw.) Ag. 



Forming lax purple tufts ; filaments abbreviated, scarcely 

 more than an inch long, not branched, varying in thickness 

 according to age ; articulations nearly equal in length and 

 breadth, sometimes only one-third as long as wide, more or 

 less constricted at the joints. 



Diameter of filaments, 28-60 //. 



Syn. Conferva atro-purpurea, Dillw. Girardia fusco-purpurea 7 

 Gray. 



Attached to wood and stones in streams more or less sub- 

 ject to tides. In Europe this plant is found also in purely 

 fresh water. 



Plate LXVII, figs. 9-11. Four sizes in different stages of 

 growth and cell division. 



Family I1LBATRACHOSPERMACEJE. 



Dioecious algse, violet, violet-purple or bluish green. Thal- 

 lus filamentous, articulate, branched, composed of a single cen- 

 tral series of cells and a secondary system more or less verticil - 

 lately branched and densely covered with simple or forked 

 branchlets. Sperniatozoids and carpogones at the ends of 

 branchlets, usually in dense orbicular clusters. Tetraspores at 

 the ends of branches. 



Genus 4, BATBACHOSPEBMUM, Both. 



Thallus moniliform, gelatinous, soft, slippery, composed of an 

 axillary or medullary series of cells, and a cortical, accessory 

 parallel series which is clothed with subglobosely clustered .fas- 

 cicles of branches which are sometimes more or less scattered. 



Mon. S. Sirodot, of France, has published a monograph on 

 LES BATRACHOSPERMES, on their organization, functions, 

 developments, etc. He points out some extraordinary differ- 

 ences of form, according to the influence of the season, the 

 supply of water, the depth at which they live and the degree 

 of illumination. According to the external conditions under 

 which they are developed, the Batrachosperms are found in 

 three different modifications, viz., I. A primordial condi- 

 tion, or prothallium; II. a non-sexual condition or Chan- 

 transia; III. a sexual condition or Batrachospermum. 



The prothallium, he says, which has hitherto been over- 

 looked by observers, is a kind of crustaceous pellicle cover- 

 ing the surface of stones on which the plant grows. It is 



