THE SLEEP OF PLANTS. 295 



it is practically certain that the phenomenon of sleep 

 is common to the whole range of both the animal and 

 vegetable creation as indeed are most of the leading 

 vital functions of our frames, such as respiration, exhala- 

 tion, circulation, nutrition, and even sensation; the 

 latter however, of course only exists in a very minor 

 degree in the vegetable creation. Plants are also 

 created male and female, and are subject to many of 

 the medical and even surgical diseases, common to 

 man and animals. Thus plants suffer from improper 

 food, sudden changes of weather, or draughts, and 

 catch cold much as we do; and of surgical ailments 

 it will be sufficient to mention tumours, warts, canker, 

 and hemorrhage. It would however involve the dis- 

 cussion of details too long and too technical in their 

 nature, to admit of going at any length into these 

 subjects in these pages. 



But as regards sleep, the fact will doubtless be fam- 

 iliar to most people that many kinds of flowers are in 

 the habit of closing upon the approach of evening ; we 

 need go no further to seek for an instance in point 

 than the common daisy, which is seen in numbers on 

 almost every garden lawn. These little flowers may 

 all be seen to close tightly up, as the sun goes down ; 

 to sleep fast throughout the night; and to awake again, 

 and expand their flowers the following morning, under 

 the influence of the solar rays. It was these move- 

 ments that the learned Linnaeus called " the sleep of 

 plants." 



It has however sometimes been supposed that they 

 were caused by cold, and were that so, it would be a 

 striking example of the existence of sensation in plants, 

 to which we have already alluded ; but this theory has 



