62 A PRIMER OF BIOLOGY 



the belief that plant protoplasm is sensitive is of 

 interest. The botanist Jung, in the seventeenth 

 century, held that a plant was a living, but not a 

 sentient organism " Planta est corpus vivens non 

 sentiens " while early in the eighteenth century 

 Linnaeus formulated his famous aphorism 

 " Minerals grow, plants grow and live, animals grow, 

 live and feel." Later still the English botanist 

 Smith postulated for plants " some degree of sensa- 

 tion, however low." In our own day biologists in 

 describing plant activities use terms derived from 

 animal life, suggested, in the first instance doubtless, 

 by superficial analogy, but justified by researches 

 which all tend to show that Smith's view was funda- 

 mentally correct, and that plants, like animals, are 

 sensitive to stimuli though perhaps the responses 

 are not in all cases so rapid or so well marked. The 

 reason for this sluggishness of response on the part 

 of the plant will appear later. George Henry Lewes 

 sums up the modern view when he says " that animal 

 and plant organisms have with their common structure 

 common properties, and if we call one of these pro- 

 perties sensitivity in animals, we must call it thus 

 also in the plant " (Arthur, " Special Senses of 

 Plants."). 



We have thus found that protoplasm, whether de- 

 rived from the plant or from the animal, is sensitive 

 to stimuli. But three things strike us at once when 

 we begin to study this subject in detail, viz., first, 

 that two stimuli, qualitatively and quantitatively 

 alike, may induce very different reactions in proto- 

 plasm of different kinds ; secondly, that the same 

 stimulus may induce very different reactions in the 

 same protoplasm at different stages of its growth 

 or under diverse general conditions ; thirdly, that 



