MARINE PLANTS. 413 



in a great measure, disappeared. The water lias ah- 

 sorbed tliem. Those who have been to the bUie Grotto 

 of Capri will remember the hght effect that lends it 

 such a magic charm. The light in the Grotto is so blue 

 because it lias passed through a considerable depth of 

 water, which has absorbed the other ra^'s. But accord- 

 ing to the physicist, Ileinrich Ka\-ser, the green Grotto 

 of Capri owes its colour to the fact that the bottom is 

 level and consists of \ellow. calcareous rock. As the 

 red rays of light are so rapidh' absorbed b\' the water 

 we can understand why red star-fish do not look red 

 but black at a certain depth. For there is no longer 

 sufficient red light to be strongly reflected h\ them. 

 Green land plants utilise chiefl\' the red , \-ellow and 

 orange cays of light in the process of assimilation. But 

 water soon absorbs these ra3's. The depth, in seas or 

 lakes, at which photographic plates are affected, gives 

 per sc little information about the possibilit\' of plant 

 life at these depths, for it is chiefl^' the blue and violet 

 rays that affect photographic plates. The rajiid disap- 

 pearance in the water ol those ra^'S necessar\ to green 

 plants would have limited the zone of vegetation still 

 more had not the Algae adapted themselves in a sin- 

 gular manner to their surroundings. Besides the green 

 colouring matter , which the landplants contain , the 

 Algae possess a red one, which enables tliem to employ- 

 other light-rays for tlie work of assimilation. These 

 plants of the deep have assumed a colour which is 

 complementary to that of the light which reaches them. 

 Those Algae, therefore, which grow in the shallows. 



