364 . Wm. Loive: 



effect a change in the colouring of various animals, but what is 

 remarkable is the subtle adaptations of Nature to the refined 

 variations of environment. This is seen in the tapeta that exist 

 in quadrupedal mammals, whose eyes are in a position to- 

 receive a great amount of reflected and transmitted rays. The 

 tapeta, which are, no doubt, needed for the protection and func- 

 tion of vision, are so varied in their colour schemes that they 

 almost rival in beauty anything that Nature has attempted for 

 the purpose of sexual selection. This fact will account for the 

 varied colour schemes that appear in the coats of animals living 

 continuously in subdued and modified sunlight, and which are so^ 

 essential for their protection. 



Chlorophyll and Plant Life. 



The object of including vegetable organisms in this discussion 

 is to show that there is a common purpose underlying the func- 

 tions of pigment in all living organisms. Vegetable pigment 

 is much more complex than that of the surface pigment of 

 animals, yet it is also designed to protect the tissues from the 

 violence of the sun's energy. 



The sun's energies are necessary for physiological processes 

 that take place in vegetable organisms, but while they are the 

 constant stimulant of these vital phenomena, over-stimulation 

 can suppress the activity of these processes and bring about the 

 ultimate destruction of the living media through which they are 

 being transmitted. Therefore, plant life is compelled to con- 

 struct a wall of resistance by which these energies can be regu- 

 lated. It is evident that this purpose is iiiainly accomplished by 

 the deposition of chlorophyll. Chlorophyll, because of its 

 colour, has the power of controlling light rays, and also because 

 of its colour and opacity, of obstructing the passage of heat 

 rays, and it therefore regulates the diathermancy of the tissue 

 involved. Its capacity in these directions will vary with the 

 density of the deposit of pigment. 



The truth of the above statements can be demonstrated, as. 

 was done in the case of animal pigments, with aniline dyes, chlo 

 rophyll pigment, or the translumination of vegetable tissues. 



