PLANTS AND ANIMALS DISTINGUISHED 223 



to move. The protoplasm of all organisms is unceas- 

 ingly active. 66 Besides this internal movement, myriads 

 of plants, as well as animals, are locomotive. Rambling 

 diatoms, writhing oscillaria, and the agile spores of cryp- 

 togams crowd our waters, their organs of motion (cilia 

 and pseudopodia) being of the very same character as 

 in microscopic animals ; while sponges, corals, oysters, 

 and barnacles are stationary. A contractile vesicle is 

 not exclusively an animal property, for the several fresh- 

 water algae, as Gonium, have it. The muscular contrac- 

 tions of the highest animals and the sensible motions of 

 plants are both due to changes in the protoplasm in 

 their cells. The ciliary movements of animals and of 

 microscopic plants are precisely similar, and in neither 

 case necessarily indicate consciousness or self-determin- 

 ing power. 



Plants, as well as animals, need a season of repose. 

 Both have their epidemics. On both, narcotic and 

 acrid poisons produce analogous results. Are some 

 animals warm-blooded ? In germination and flowering, 

 plants evolve heat the stamens of the arum, e.g., 

 showing a rise of 20 F. In a sense, an oak has just 

 as much heat as an elephant, only the miserly tree locks 

 up the sunlight in solid carbon. 



At present, any boundary of the animal kingdom is ar- 

 bitrary. " We cannot distinguish the vegetable from the 

 animal kingdom by any complete and precise definition. 

 Although ordinary observation of their usual representa- 

 tives may discern little that is common to the two, yet 

 there are many simple forms of life which hardly rise 

 high enough in the scale of being to rank distinctively 

 either as plant or animal; there are undoubted plants 

 possessing faculties which are generally deemed charac- 

 teristic of animals ; and some plants of the highest grade 

 share in these endowments." 67 



