Nov. 1898.] BOTANICAL SOCIETY OF EDINBURGH 123 



Life originated in the sea, either on the surface of the 

 deep sea or on the coast, and there is no doubt that the 

 earliest organisms were unicellular algre, and that the next 

 organisms were also alga-, but multicellular. 



The life work of alga' is to fix, by means of sunlight, 

 the carbon derived from the carbonic acid of the ocean 

 water. The alg;e probably appeared not very long after 

 the earth's surface cooled below 212°, so as to allow of 

 water existing. For a long time they inhabited a sea of 

 almost equal temperature, for even after the cooling of the 

 earth the equatorial ocean currents would keep the poles 

 warm. At first, reproduction was simply equal division, in 

 obedience to Herbert Spencer's law, of the surface being as 

 the square, and the contents as the cube. 



But the law of fortuitous variation was also at work, 

 and as long as the ocean contained but few organisms, it 

 was but little checked by the law of natural selection ; so 

 that there would be many varieties, but no species, for it 

 is fortuitous variation that causes varieties, natural selec- 

 tion that makes species, by killing the intermediate 

 forms. 



You will observe, however, that these alga? were in very 

 different positions, according as they lived near the equator 

 or near the poles. 



At the equator an organism worked, like a day labourer, 

 for twelve hours, and then rested for other twelve. 



At either pole, an organism had six months of con- 

 tinuous work, followed by six months of rest, though the 

 temperature in the two places was practically the same. 



Eeproduction by equal division was all very well at the 

 equator, but things were very different at the poles, and it 

 was there, no doubt, that the more complex forms of 

 algoid reproduction appeared. 



I may enumerate the forms of reproduction which now 

 exist among alg?e — 



1. Simple equal division. 



2. Budding. — This may have taken place at the equator 



as well as at the poles. 



3. A resting Spore, which slept for the six winter months, 



and became an alga? when the summer returned. 

 This is evidently of polar origin. 



