3 26 PHILOSOPHICAL NOtKS OX 



examples of microbes, which, far from being harmful to their 

 foster-parents, are exceedingly useful, and help them in the 

 struggle for existence. Indeed, i3arasites, even in our own bodies, 

 perform a good bit of our physiological work, and probably we 

 would die of starvation without them ! 



Such may have been the spiral microbe, which, once upon a 

 time, may have become parasitic on what we now call the cellular 

 plant, and entered into co-operative association with it. The 

 development of this microbe we noAV call the vascular system of 

 plants. The spiraliiy of this microbe would have given rise to a 

 tube, through which the sap could better circulate than in the 

 simple intercellular spaces, liable to be encroached upon and 

 compressed by the growing and multiplying parenchymatous cells. 



The parasite which rots timber finds no difficulty in ramifying 

 itself between the cells of the solid wood.* Much less difficulty 

 would this conjectural spiral microbe find in growing and 

 ramifying itself through the sappy interspaces of the cells of 

 plants. 



Fantastic as this hypothesis of the genesis of the vascular 

 system in cellular plants may at first sight appear, it is borrowed 

 from facts relating to microbes and the mycelia of fungi, the 

 operations of which, at first sight, may also have appeared as 

 fantastic. 



After all, the whole of life seems nothing but the multiplication 

 and development of microbes — some feeding on others and 

 destroying them, some feeding on others and helping them to live 

 and flourish. 



It appears established that more kinds than one can live 

 peacefully together, and help each other within the precincts of the 

 same family, thus forming one structure out of two or more 

 originally distinct and separate structures. 



In such a case the order of evolution would be — first, a 

 differentiation in monojihyta, or one-celled bodies, with the 

 result of a struggle, and a natural selection, even in living things 

 so simple as these. This has, I think, been clearly proved by 

 Dr. DalHnger in his experiments on monads. 



♦ I believe this is now explained by the parasitic rootlets exuding a 

 ferment, which dissolves and softens the ■wood through A\hich they pass. 



