ON THE PHYSICAL BASIS OF LIFE 103 



forms of life, which people an immense extent of the 

 bottom of the sea, would not outweigh that of all the 

 higher living beings which inhabit the land put together. 

 And in ancient times, no less than at the present day, 

 such living beings as these have been the greatest of 

 rock builders. 



What has been said of the animal world is no less 

 true of plants. Imbedded in the protoplasm at the 

 broad, or attached, end of the nettle hair, there lies 

 a spheroidal nucleus. Careful examination further 

 proves that the whole substance of the nettle is made 

 up of a repetition of such masses of nucleated proto- 

 plasm, each contained in a wooden case, which is modi- 

 fied in form, sometimes into a woody fibre, sometimes 

 into a duct or spiral vessel, sometimes into a pollen 

 grain, or an ovule. Traced back to its earliest state, 

 the nettle arises as the man does, in a particle of 

 nucleated protoplasm. And in the lowest plants, as in 

 the lowest animals, a single mass of such protoplasm 

 may constitute the whole plant, or the protoplasm may 

 exist without a nucleus. 



Under these circumstances it may well be asked, how 

 is one mass of non-nucleated protoplasm to be dis- 

 tinguished from another? why call one "plant" and 

 the other "animal"? 



The only reply is that, so far as form is concerned, 

 plants and animals are not separable, and that, in 

 many cases, it is a mere matter of convention whether 

 we call a given organism an animal or a plant. There 

 is a living body called jEthalium septicum, which ap- 

 pears upon decaying vegetable substances, and, in one 

 of its forms, is common upon the surfaces of tan-pits. 

 In this condition it is, to all intents and purposes, a 

 fungus, and formerly was always regarded as such ; but 



