RHODOSPERME®. 213 
on the calcareous alge in deep water, whence its specific name of parasitica. 
It is sometimes found growing on the sheltered sides of ledges of rock, at 
the extreme limit of low water, and occasionally it is cast ashore in fine 
- condition. Several years ago I found some lovely specimens of this rare 
Polysiphonia on the beach at Whitley, near Tynemouth. I have also 
taken it in Scotland and at Plymouth. The illustration is from the most 
perfect of my south Devonshire specimens. Under the microscope a branch 
of this species is a singularly beautiful object. The ramification of its 
closely set branches is perfectly regular. They are placed on each side of 
the stem in alternate series; the same order being observed throughout 
the entire plant. The tubes in the articulations, when viewed longi- 
tudinally, appear to be pointed at both ends, and are separated by 
transparent or colourless spaces. The siphons are eight in number, sur- 
Fig 106. Polysiphonia parasitica, magnified. 
rounding a narrow cavity. A transverse section of the stem is seen 
at d, Fig. 101. The fronds of this rare little plant rarely exceed 3in. in 
height, but they are found sometimes in such densely bushy tufts, 
that a skilful manipulator may easily make several lovely book specimens 
from a single plant—no small advantage when the rarity of this species is 
considered. It is, however, widely distributed, being found in Scotland 
and as far south as the coast of Cornwall. P. byssoides is so named 
from the multifid byssoid ramuli with which the branches are clothed 
throughout. Dr. Harvey says, ‘‘ these terminal branched ramuli may 
probably be regarded as leaves in an imperfect state of development. 
In other species they are only found on the tips of young fronds, and 
appear to be actively engaged with the growth of those parts; and while 
