Seaweeds and Leaf-green 



It was made to grow behind specially contrived screens 

 of coloured glass, and the results were as follows ; — 



Behind red glass, that is, in red light, it became green. 



„ green „ green „ more or less red. 



„ blue „ blue „ brownish yellow.^ 



This shows that Oscillatoria is able to produce what- 

 ever colour suits itself best, which is a most important 

 discovery. But how is it that the wave-lengths of one 

 colour set up in Oscillatoria a substance which gives 

 out the vibrations of the complementary shade ? 



This is, however, an instance of what we may call a 

 "fitting reaction" directly produced by the conditions 

 and useful to the plant. No one, not even Maeterlinck, 

 would suppose that oscillatoria had studied optics and 

 intentionally manufactured the green or red, but still the 

 colour is produced. 



Plant life must have commenced at some period in 

 the history of the earth. There was a time when the 

 world seems to have been nothing but gas and mist at 

 a very high temperature. Even in such early geological 

 times as that of our Coal Measures, many plants, and 

 some of them very highly organised, were in full activity. 

 Even then, some authors suppose that the whole ocean 

 had an average surface temperature of 70° F. (21° C), 

 and that there was no cold water either in the Arctic 

 or Antarctic Seas.' 



Many algae would thrive in hot water of this tempera- 

 ture. Indeed, from what we know of the endurance of 

 living protoplasm, it would be very difficult to say what 

 degree of heat would necessarily destroy all vegetable life. 



Even to-day algae are said to flourish and grow well 

 in certain very hot springs. The water in those at 

 Karlsbad is at 70° C, and in the baths at Las Trincheras, 

 Venezuela, 80° C.^ Some doubt has been expressed as 



33 c 



