1G4 OXALIDE^ 



had been made, found that the plant must be teased for a long time, as its 

 movements are much slower than those of the Mimosa. This botanist 

 believed, from various observations which he had made on sensitive plants, 

 that heat was the principal agent in this phenomenon, as he observed 

 that that most singular of plants, the moving saintfoin {Hedysarum gyrans), 

 moved less during winter in hothouses. This writer considers that all 

 the species of Oxalis are susceptible of contraction when irritated ; but 

 as a large number of the cultivated species are from the Cape of Good 

 Hope, they show no effects from concussion in our atmosphere, whose 

 greatest heat is never equal to that of Africa. Professor Morren fur- 

 nished several interesting notes on this phenomenon, which subsequently 

 led to a discovery of some analogy in structure between the leaves of the 

 Wood-sorrels and those of the Mimosa', an analogy quite unexpected by 

 botanists, but which subsequent observation has fully established. One very 

 remarkable peculiarity belongs to the Wood-sorrels, which is, that M. de 

 Candolle was never able to modify the closing of these leaves at night, as 

 he did those of many plants, by the alternation of artificial light with dark- 

 ness ; whence he inferred that the folding up of the leaves, termed the sleep 

 of plants, and their unfolding, or awaking to the light of day, were connected 

 with a periodical disposition of motion inherent in the plant. In the case, 

 however, of Oxalis acetosella the attitude of the sleeping leaf is at once 

 assumed when bright sunshine suddenly falls upon it. 



The irritability of various plants, and the nightly folding of many, has 

 occupied the attention of botanists, from Linnneus to those of our own day, 

 and anyone at all accustomed to observe the flowers, either of the garden 

 or the country landscape, must have seen it. Plants possess three distinct 

 kinds of irritability, namely, such as depend on atmospheric phenomena, 

 spontaneous motions, and such contractions as are caused by the touch 

 of other bodies. Our Wood-sorrel exhibits two of these influences, but we 

 have scarcely any native plant which shows any great degree of spontaneous 

 movement, except the Oscillatorias, which are weeds of our fresh or salt 

 water, and whose thread-like forms twist about like worms, and move to 

 a considerable distance from the spot on which they are laid. The moving 

 saintfoin of the East Indies is the most remarkable of all plants for its 

 perpetual restless movement by day and night. 



The sleep of plants is not confined to the folding of their leaves. As 

 twilight approaches, many flowers alter their position. Sometimes the leaves 

 fold over the delicate petals, so as to shield them from nightly dews, or the 

 hoar frosts of spring or chilly blasts of autumn. Many flowers close quite up 

 during night. The daisies, which sprinkle our meadows, received their pretty 

 name from their opening only to the morning light, and many, like Chaucer, 

 mark them thus folded on the mead — 



" When that the sunne out of the south gan west, 

 And that this floure gan close and gon to rest." 



Flowers of the rayed form are peculiarly so affected, and are like "The 

 marigold that goes to bed with the sun, and with him rises Aveeping." 



Even the corn-field shows its sensitiveness to the approach of the shadows 



