The Substance Which Is Alive in Plants 149 



world, and that all protoplasm nowadays originates from pre- 

 existent protoplasm through reproduction. This much is easy. 

 But when we try to trace back the continuously-reproducing 

 chain to its very first origin in time, we come soon to the limits 

 of our knowledge. Some philosophers have suggested that the 

 germs of life were first brought to the earth in meteorites from 

 other planets; but this merely sets back the difficulty one stage 

 and does not remove it. Another explanation, which seems to be 

 that most commonly assumed by scientific men, places its origin 

 in spontaneous generation at some time in the earth's history 

 when the favorable combination of material and energy happened 

 to occur. Obviously, such a combination ought to be repeatable 

 experimentally; and it is upon this assumption that many learned 

 men, from astrologers of old to physiologists now with us, have 

 sought, though in vain, to make protoplasm anew in the flasks 

 of their laboratories. There is, however, a third explanation which 

 I have already suggested in an earlier chapter, namely, that the 

 protoplasm known to us did not originate in its present form, 

 but is evolved or descended from a simpler substance adapted 

 chemically to the higher (or lower) temperatures which formerly 

 prevailed on the earth, while that substance in turn was evolved 

 from a still simpler, and so on backwards to a beginning cotempo- 

 raneous with that of inorganic matter itself. This view I hold 

 to be the most reasonable and probable. 



But, after all, the most impressive and important thing about 

 protoplasm is its power to build those great and elaborate struc- 

 tures which we call plants and animals. For, structurally con- 

 sidered, a plant or an animal is nothing other than a mass of 

 soft protoplasm which climbs aloft and reaches outward into the 

 form of the plant or the animal, building itself meantime a skele- 

 ton for the support of its helplessly-weak substance. Now, in 

 building these organisms, the protoplasm never exhibits the char- 

 acter of a continuous and homogeneous mass, but always sepa- 

 rates partially into tiny structural units called cells, which are 



