98 



THE YOUNG NATURALIST. 



resembles the nightly sleep of animals, 

 but, as we bare night-roaming beasts and 

 birds, so we have night-blooming flowers, 

 as the evening primrose (Enothera biennis), 

 and the night-flowering catch-fly (Silene 

 noctiflora), which is not uncommon as a 

 weed of cultivated fields, and the creamy 

 white petals of which are curiously rolled 

 up during the day but expand at night. 

 In a closely allied species, the evening 

 Lychnis (L. vesper Una) , which is frequent 

 in dry sandy corn-fields, the beautiful 

 large white fragrant flowers expand in 

 the evening twilight. Not only are they 

 less active, but there is a considerable 

 change, in the character of the vital 

 functions of plants during darkness. For, 

 whereas in bright sunlight, plants 

 greedily absorb carbonic acid gas — one 

 of the most pernicious products of animal 

 life — and evolve oxygen. In darkness 

 this process is reversed, and plants con- 

 sume oxygen and liberate carbonic acid 

 gas, same as animals do when breathing, 

 and it is only the comparative cessation 

 of their functions during their nightly 

 sleep which prevents them having a 

 deleterious effect upon the atmosphere. 

 During darkness all plants become less, 

 or more limp and flaccid, by the with- 

 drawal of water from their tissues, so 

 that their leaves often droop and hang 

 down, as is well seen in the little wood 

 sorrel and several commonly cultivated 

 species of the same natural order (czalid- 

 acece). In the similar trifoliate leaves of 

 common clover the leaflets fold upwards 

 at night. So sensitive are certain plants 

 to the influence of light that the mere 



shadow of a moving cloud in a bri 

 summer day passing over a field of bea 

 will cause a sensible deflection of 

 leaflets. Doubtless the most popu 

 idea of the sleep of plants is furnish 

 by the periodical opening and closing 

 their blossoms. This has long been < 

 served, and attempts have been made 

 construct a floral clock, by arrangi 

 plants according to the time of expar 

 ing or folding of their flowers. Althou 

 perhaps there is no hour of the day 

 night which is not marked by the openi 

 or elosing of some flower, yet the mi 

 imum of opening or waking flowers see 

 to be attained between six and eight 

 the morning, and the greatest numl 

 close or go to sleep between four and $ 

 in the afternoon. Certain plants are 

 regular in their hours as to have derfv 

 their common names from this peculiari 

 The yellow goat's beard (Tragopog 

 pratensis ) is known to every school-b 

 as Jack-go-to-bed-at-noon ; the ever w 

 come flower of childhood, the daisy (da 

 eye), so called from its flowrets expandi 

 with daylight, but closing at nightfall, 6 

 These periodic movements seem due tc a 

 variety of causes,' such as the humidi" 

 of the atmosphere. The scarlet pimperi 

 (Anagallis arvensis) is called the pc 

 man's weather glass, because its flow 

 remain closed when the air is saturat 

 with moisture and rain is about to h 

 Some can be stimulated to wakefulnf' 

 by artificial light ; the common yell 

 crocus will expand its blossoms unc 

 gas or candle light, and the same 1 1 

 been observed in the spring genti I 



