(36) 



We have followed Professor Hai-vey in retaining this curious species 

 in the genus Desmarestia, without being perfectly satisfied that we have 

 done right in so doing. It will be seen that it differs very considerably 

 in structure as well as in habit from the other species of the genus, 

 resembling them only in the delicate confervoid filament which forms 

 the axis ; the coating of minute cellules which suiTounds it being greatly 

 extended, and when a section is made near the base of the stem, occupy- 

 ing fully two-thirds of the radius, and being moreover abundantly 

 interspersed with lai-ge roundish or oval cells which are empty, the 

 remainder of the diameter being composed of much larger cells, becoming 

 somewhat smaller towards the surface, but without the periphery of 

 minute cells which characterises the other species of the genus. In the 

 young state this coating of cells is moreover entirely wanting, the 

 slender filaments being composed of the single-jointed filament of the 

 axis, which gradixally becomes covered by the cells as the plants advance 

 in age. 



Its remarkable property of changing colour is not one of the least 

 curious circumstances in its history. This jjroperty we have seen it 

 manifest in less than half an hour after removal from the water. Dr. 

 Harvey has pointed out its resemblance to Dictyosiphon, and observes 

 that they may be at all times distinguished by the constantly opposite 

 branches of the present species. 



DF.SMABESTIA VIRIDIS. 



EXPLANATION OF DISSECTIONS. 



Fig. 1. — Apex of young frond. 



2. — Transverse section of the stem. 



3.— Portion of stem partly covered by cellules. All magnified. 



