166 TEANSACTIONS LIVEEPOOL BIOLOGICAL SOCIETY. 



or to act as a shield against the excess of green and blue 

 rays penetrating the water. This is a subject for experi- 

 ment which I venture to urge upon the attention of plant 

 physiologists since it cannot but prove fertile in results. 

 To pursue our excursion into the depths, it may be noted 

 that very few forms are to be found between 50 and 100 

 fathoms, and beyond, hardly any. Phyllophora Brodicei 

 and several other Algse (excluding diatoms and calcareous 

 Algse which are brought up dead from great depths to 

 which they have been drifted) have been recorded from 

 greater depths than 100 fathoms, but the records are open 

 to question. It is quite safe to place the absolute limit at 

 200 fathoms. The fact just alluded to that the quality of 

 the light is affected by its passage through the water 

 probably explains in part why Algse do not go to a greater 

 depth since light penetrates much farther. Of course 

 other causes, such as pressure, etc., may operate also in 

 this direction. We see then that the range in depth of 

 marine Algse is slight as compared with that of marine 

 animals, in this respect affording a significant contrast 

 with the relative distribution of the land flora and fauna, 

 which I suppose may be said to have the same frontiers. 

 It would be easy to support the statement that light is 

 the regulator of the zonal distribution of Algse by numerous 

 observations, if these were necessary. I may cite one as 

 a sample. It is well known that certain deep water 

 species are frequently found near the surface, under shelter 

 of dark rocks and caverns, which, at all events, proves that 

 pressure has little to do with the matter, at least within 

 comparatively narrow limits. Against this view of the 

 high susceptibility displayed by Algse, to the amount and 

 nature of the supply of light I am bound to cite one 

 staggering fact. Kjellman observed that in the polar sea, 

 during the dark arctic night of three months duration 



