The Action of Light on Chlorophyll. 



397 



in large quantities in the solution. I therefore placed equal quantities of a 

 light blue iodine-coloured starch solution in two test-tubes. To one of these 

 I added distilled water ; to the other an equal quantity of the slimy liquid 

 obtained by soaking pieces of the frond of laminaria in water. The colour 

 disappeared at once, on shaking up, in the tube containing the slime, but not 

 in the tube to which distilled water only had been added. I then placed equal 

 quantities of a very dilute iodine solution (iodine in potassium iodide) in two 

 test-tubes. To one I added, as before, distilled water, to the other an equal 

 quantity of the slimy liquid from laminaria. These were then shaken and 

 left to stand for a short time. Equal quantities of a dilute starch solution 

 were then added to each, with the result that the blue coloration appeared 

 in the tube to which distilled water had been added, but no coloration at all 

 in the tube containing the slime. 



These experiments show, therefore, that iodine is absorbed by the laminaria 

 slime, probably forming an additive compound with it, and it appeared 

 probable that a much more satisfactory iodine reaction would be obtained 

 with laminaria if the frond were first of all freed from slime by washing well 

 in water. I obtained the reaction very readily on a bright spring morning on 

 the sea-shore by placing pieces of the fresh frond free from slime in contact 

 with starch paper. The reaction is, however, very unequal ; all parts of a 

 frond are capable of giving it, but not necessarily at the same time. The 

 most vigorous reaction was obtained in the growing region of the frond, the 

 swollen portion where the frond joins the stipe. The reaction appears to be 

 associated with those layers of cells which contain the chlorophyll and the 

 brown colouring matter. Sections of the stipe and of the thicker portions of 

 the frond, when placed in contact with starch paper, showed a blue layer all 

 round where the paper had been in contact with the peripheral chlorophyll- 

 containing cells, and sections from the thinner portions of the frond also 

 gave the same result. 



Pieces of the frond kept in sea-water in the dark gave no reaction, or at 

 times a slight one ; a strong reaction was obtained when the fronds had been 

 exposed to a good light. The presence of the slime, however, may prevent 

 the reaction. So long as any of the brown colouring matter is present, the 

 iodine reaction may be given, but it is entirely absent in those parts of the 

 frond which have lost the brown colouring matter and show a green colour. 

 Whether the iodine reaction is associated with the brown colouring 

 matter I cannot say, but if one half of a piece of frond is placed for a short 

 time in hot water to destroy the brown coloration, the iodine reaction is 

 obtained only with the brown portions of the frond. 



It is probable, therefore, though not quite certain, that the action of light 



