Closterium Ehrenbergii. 3 



delicate mucus is secreted around the approximated fronds ; these 

 remove to a little distance from each other, undergo " self-divi- 

 sion," and present altogether an irregular oval figure, the outline 

 of which is formed by the periphery of the mucus, the four divi- 

 sions of the fronds being placed in the middle in a somewhat 

 quadrilateral manner (fig. 3). During the progress of self-divi- 

 sion the internal membrane of the cell-wall becomes enlarged 

 at the suture or line of separation, and projects in the form of 

 an irregular cone with a blunt or rounded apex forming a beak, 

 whose side view presents a triangular outline. This beak be- 

 comes filled with endochrome, either by the dilatation or increase 

 of the contents of the half-frond, and the divided frond assumes 

 the appearance of one with two unequal segments, being what 

 M. Morren calls " une Closterie a deux cones inegaux w (fig. 3) . 

 On these membranous expansions, at the concave surfaces of the 

 fronds and close to the original sutures, there appear, almost 

 simultaneously with the formation of the beaks, two circular 

 projections, which rupturing at their apices, give egress to the 

 delicate sacs which inclose the endochrome, and which drawing 

 with them their contents and meeting with the endochrome-sacs 

 emitted through similar projections from the other half-fronds, 

 form by their connection irregular masses which quickly conso- 

 lidate and assume the appearance of perfectly circular, smooth 

 dark-coloured balls, the sporangia of Ralfs and seminules of 

 Morren (figs. 4, 5). 



The discharge of the endochrome and formation of the spo- 

 rangia are accomplished with much rapidity, and may often be 

 seen taking place in the field of the microscope, the whole ope- 

 ration not occupying more than a few minutes. It will be seen 

 from an inspection of the figures, that during the formation of 

 the sporangia there appears to be a second development of mu- 

 cus in the form of rings around the reproductive bodies ; this is 

 probably only the effect of the pressure produced by the growth 

 of the sporangia on the mass of investing mucus. It will also 

 be seen that the pale transverse band adopted by Ralis as a cha- 

 racter of the genus Closterium, and which in figs. 1 and 2 occu- 

 pies the centre of the undivided frond, is, upon self-division 

 taking place, removed a little towards the extremities of the half- 

 fronds (fig. 3). The reason as well as the cause of this motion 

 I am unable to explain, but it seems to confirm the propriety of 

 adopting the band itself as a permanent and important cha- 

 racter. 



With regard to the subsequent changes which take place in 

 the sporangia, the time which elapses before they produce young 

 fronds, and the mode in which such evolution of a fresh race is 

 accomplished, I have not been fortunate enough to ascertain any- 



1* 



