DIFFERENCES IN ANIMAL AND PLANT LIFE 513 



of the great majority are expended during the whole of their 

 adult life. The greater part of the higher vegetal life in 

 temperate climates can be said to rest for half the year, and it 

 may well be that this annual period of quiescence, during which 

 the tree merely absorbs sufficient nutriment to preserve its 

 vitality, is one of the causes of its long life. 



All land plants are anchored to the soil or rock on which 

 they grow and have no free conscious movement. It is true 

 that many vegetal spores are motile. Those of Vaucheria 

 rotate with a screw-like motion on their longer axis, but this 

 movement of plant spores is different from the swimming of 

 animals in the water, and it may possibly be accounted for by 

 an absence of symmetry in the molecular arrangement of the 

 protoplasm of which they are composed. Plant spores, for the 

 rest, are only temporarily motile, and are in transition to 

 the plant state to which they essentially belong. If the 

 spermatozoids of certain plants resemble those of animals, the 

 resemblance is no cause for concluding that they are much 

 nearer to animal life than their development shows them to be, 

 and if insectivorous plants have not their internal cavity fully 

 developed, they are none the less rooted to the soil, and derive 

 a portion of their nutrition from it. They have been known 

 to exist for as long as two years without animal food. 



Mobility affords irrefragable proof of life, but whereas in 

 animals it is almost always perceptible or easily excitable, 

 in plants (excepting in the spore phases above alluded to) it 

 may be said to be absent — the leafing of trees and the extension 

 of roots being in reality phenomena of growth. If an animal, 

 like a plant, were chained to one spot without the power of 

 movement it would slowly perish although supplied with food 

 and going through physiological exchanges with the outer 

 world. The adult plant, on the contrar}', thrives in immobility. 

 On the part of plants there is no conscious search for food unless 

 it be in the faintest manner by the roots. The plant accepts the 

 nutriment which the soil offers in which it is able to grow as 

 well as the moisture which the rains provide. If moisture is 

 withdrawn from the site on which it stands, then death ensues, 

 since the plant, unlike the animal, cannot remove to more favour- 

 able pastures, and must share the fortunes of its environment. 



In the matter of nutrition there is a considerable difference 

 of process. In plants all food is taken in a soluble form, for the 



