Laminaria digitata and Laminaria saccharina. 179 
L. saccharina , the lamina consists of one long tapering lobe, the central 
portion of which is somewhat corrugated. 
Both species contain a mucilaginous substance in their tissues ; this is 
slightly soluble in distilled water, and readily soluble in alkalies : from an 
alkaline solution it is reprecipitated by acids as a gelatinous substance. 
The colouring matter, to which the plants owe their olive-brown tint, 
is contained in the chromoplasts of the cells of the parenchymatous layers. 
Besides chlorophyll they contain a pigment, known as phaeophyll: this 
can be shown to consist of two substances, phycophaein and phycoxanthin, 
the former soluble in distilled water, the latter in alcohol (West). Neither 
phycophaein nor phycoxanthin gives distinct absorption bands in the spectrum. 
Both are readily decomposed by the action of light, and in the process 
of decomposition become first of a pale green tint, and finally colourless. 
The reproductive areas of L. digitata occur as cloudy patches ol 
irregular shape and size, situated on the older portions of the lamina, that 
is, towards its distal extremity. The areas vary in colour from a light 
brown to a brownish black, and are slightly raised above the surrounding 
surface ; in most cases each corresponds in size and position with a similar 
area on the other side of the lamina. The colour appears to depend on the 
ripeness of the reproductive organs, which darken as they become more 
mature. In L. saccharina similar patches are found, but they are more 
extensive and usually continuous. They form a very dark area which 
extends along the greater part of the lamina, but is chiefly confined to the 
central corrugated portion. In the neighbourhood of Plymouth, plants 
of L. digitata bearing mature reproductive areas are common during the 
months of October and November, and those of L. saccharina a few weeks 
later. 
Methods. 
Collection of specimens. 
The most satisfactory results were obtained with plants collected 
in situations free from any possibility of contamination by river water, 
sewage, &c. In the neighbourhood of Plymouth, the best plants were 
obtained from Wembury Bay, where they grow in great profusion, and are 
relatively free from growths of other Algae, which are so often found on the 
thallus of Laminaria. Culture experiments with plants obtained from 
within Plymouth Sound resulted in such plentiful growth of Bacteria, that 
the water rapidly became thick and cloudy, and portions of the thallus 
in the culture solution soon decomposed. 
Preservation of living specimens. 
Under normal conditions most of the larger Algae retuse to grow 
in the Laboratory tanks. Mature specimens of any of the Laminariaceae 
or Fucaceae soon die and begin to degenerate. On the other hand, most 
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