1 94 JOHN H. WILSON [makoh 



its " feat." It is a harmless creature compared with one we read 

 of next : — 



Fierce in dread silence on the blasted heath 



Fell Upas sits, the Hydra-Tree of death. 



Lo ! from one root, the envenom 'd soil below, 



A thousand vegetative serpents grow ; 



In shiny rays the scaly monster spreads 



O'er ten square leagues his far-diverging heads. 



Although we must not expect to find anything so very sensational 

 as this in our study of vegetable motility, it is not without its surprises. 

 Who, on first seeing the Sensitive Plant shrink from touch, has not 

 exclaimed, " How very wonderful ! " or failed to follow up the ejacula- 

 tion by the query, " How does this extraordinary movement take 

 place ? " 



The sensitive plant most commonly grown in greenhouses is Mimosa 

 pudica ; other species, some of which are only slightly " sensitive," are 

 seldomer seen. The common species is easily grown from seed which 

 can be purchased, or gathered from plants which have flowered indoors. 

 Like many of its congeners it performs the so-called sleep movements, 

 closing up and lowering its leaves at night. During the day the leaves 

 are spread out flat. If, then, a leaflet at the extremity of the divided 

 leaf is touched lightly, in an instant the pair of leaves contiguous to it 

 will flap upwards and meet, then the next pair, and the next, until the 

 whole series approximate. If the stimulus is sufficiently strong, it 

 will pass into the neighbouring secondary leaf-stalks, and not only 

 cause the leaflets they bear to meet, but will induce the leaf-stalks 

 themselves to come together, like the ribs of a fan when being folded 

 up. It is quite possible, with caution, to cause one leaflet alone to move 

 without affecting any of the others. When the stimulus has been 

 severe, the folding up of the leaflets is followed by the drooping of the 

 primary leaf-stalk. A rude shock causes the whole foliage of the 

 plant to assume instantly a collapsed and dead appearance. It is a 

 mistake to suppose that the approximation of the leaflets must take 

 place before the fall of the hinged stalk. By gently pressing on 

 the top of the stalk it can be made to descend without disturb- 

 ing the leaflets at all. It is noticed that the leaves are more 

 sensitive at a certain stage of their growth than later, and that 

 the maximum degree of irritability is reached at a certain period of 

 the day. 



Eecovery is gradual, not sudden, the time taken in the process 

 varying with the age of the leaf and the intensity of the light. 

 Elaborate investigations have shown that the motile power is 

 centralised in the swellings at the base of the leaflets and leaf-stalks. 

 The fluids filling the cells of one side of the cushions are suddenly 

 transferred to the opposite side, the equilibrium is disturbed, and the 

 leaflets or leaf- stalks must needs move in the direction of least 



