There is no British alga with which this beautiful plant can well 

 be confounded. The extreme delicacy of its capillary ramuli, 

 the constantly exact opposition of all its parts, from the primary 

 •branches to the most minute of the decompound ramuli (the last 

 of which are much finer than the most slender hair), and the ver- 

 satile colour, are all marks which peculiarly belong to Desmares- 

 tia viridis. Old and weather-beaten fronds, which have lost the 

 more delicate ramuli, have something the aspect of Bictyosiplton 

 fozniculaceus, but may at once be distinguished by the opposite 

 branching. 



At Fig. 2 I have represented the magnified appearance of one 

 of the growing points of the young frond, showing the gradual 

 coating of the confervoid frame-work (or skeletoii) of the frond. 

 It mil be seen that all the younger portions consist of a simple 

 string of cells, or articulated filament, and that in the lower part 

 these cells are coated by a stratum of much smaller cellules. As 

 the growth proceeds these external coats are constantly increased, 

 while the original central skeleton may still be traced, through all 

 the branches, and even in the stem, a section of which is seen 

 at Pig. 3. 



B. viridis is very widely dispersed through the colder zones, 

 both north and south, and increases in luxuriance as it ap- 

 proaches either pole. 



Fig-. ]. Desmarestia viridis : — the natural size. 2. A growing apex of a 

 young branch : — highly magnified. 3. A transverse section of the stem : — 

 magnified. 



