122 
NATURE NOTES. 
support relatively few forms, owing tothe bad holding ground for 
the anchoring holdfasts of seaweeds. A shelving, rocky shore, of 
which much is exposed at low water, like that of Berwick-upon- 
Tweed, is always the best collecting ground. At high-water 
mark and near it there will be found mostly green forms of the 
same colour as land vegetation ; lower down, between tide marks, 
a profusion of the olive Algae sheltering red ones beneath them. 
At low-water mark and beyond it the olive-brown hue predomi- 
nates, and it also shelters red seaweeds, which go deepest of all. 
If we take home any of these olive or red sea-weeds and put 
them for a time in fresh water, they w'ill become green like those 
at high-water mark ; but no amount of fresh water will alter the 
green colour. If we now put them into spirit (and some of the 
originally green ones as well) we can dissolve out the green colour. 
We learn from this that the olive and red seaweeds have two 
kinds of pigment — one, olive or red soluble in fresh w'ater, and the 
other, green, soluble in spirit. All plants, except fungi and 
parasites and the like, have this green colour, and as we know, 
it is the principal agency in the process of nutrition. In the 
presence of sunlight it enables the plant to convert the inorganic 
substances on which it feeds into plant substance. What then 
is this added olive or red colour that we find in seaweeds between 
tide marks and below ? How is it useful to these sea-plants? 
We know that the great depths of the sea are quite dark, no 
ray of light penetrates into this pitch black world inhabited by 
luminous animals, often of grotesque form, fitted to withstand 
the tremendous pressure of the water. There are no seaweeds 
down in this darkness ; they need the light of the sun. If we 
could descend in one of M. Jules Verne’s appliances we should 
find this total darkness begin somewhere about 700 fathoms ; 
probably before that, but in the gloom between 50 fathoms and 
700 there would be no seaweeds — or very, very few immediately 
below the 50 fathom line. We might come upon some detached 
specimens washed down in a submerged current. How is it, then, 
that there are no plants even in this twilight ? Is it pressure ? 
for plants can certainly grow with very little light. We might 
hazard a considerable number of such reasons, but the true one 
is this. The sea water absorbs the light, producing darkness as 
we have seen, but it also intercepts some rays very quickly 
indeed, permitting others to pass farther into the depths, and 
thus affects the quality of the light. Those first intercepted are 
precisely the rays most efficient in appealing to the green 
colouring matter of vegetation, and in their absence or diminished 
supply, plants either cease to exist, or do so with a special 
provision for the purpose. We may fairly conclude, then, that 
these added colouring matters, olive and red, are adaptations 
to this diminished supply between tide marks and immediately 
below low-water mark, and that even with such help sea- 
weeds cannot penetrate very far. Whether these added colours 
heighten the susceptibility of the green colour to a diminished 
