250 Rev. P. Keith on the Susceptibilities of Living Structures. 



meet together on the upper side of the leaf-stalk. The first 

 case is exemplified in the leaflets of the common Acacia, Aca- 

 cia pseudacacia : the latter in the leaflets of common clover. 

 This phaenomenon, as occurring in the night, received from 

 Linnaeus the appellation of the Sleep of Plants. — 4thly. The 

 flowers of many plants are also susceptible to the stimulus 

 of lio-ht, and do not fully expand their petals except when the 

 sun shines. The Papilionace(e expand their delicate wings 

 only during the light of day, and close or fold them up again 

 as the darkness of the night approaches. But the most sin- 

 gular case of this kind is, perhaps, that of the Lotus of the 

 Euphrates, as described by I'heophrastus *. The flower of 

 this celebrated plant, which floats on the stream during 

 the day, closes and sinks down beneath the surface of the 

 water during the night, so as to be beyond the grasp of the 

 hand, and emerges, and rears itself up again in the morning, 

 to present its lovely and expanded petals to the sun. — But 

 though many plants open their blossoms during the day, yet 

 all do not open them at the same time. Some^ open them at 

 sun-rise ; some not till the sun has attained a considerable 

 altitude ; others not till noon. This sequence in the time of 

 the opening of the blossom has been designated by botanists 

 the Horologium Florce. — 5thly. The vegetative powers of the 

 plant which have been dormant during the colds of the winter 

 begin again to revive, and to resume their wonted activity 

 as the warmth of spring advances, forwarding the process of 

 germination, and the protrusion of the leaf and flower, and 

 the development and maturation of the fruit, according to the 

 season or temperature proper to each species. Thus the 

 honeysuckle protrudes its leaf in the month of January; the 

 gooseberry, currant and elder, in the end of February or 

 beginning of March; the willow, elm and lime-tree in April; 

 and the oak and ash in May. A similar sequence takes place 

 in the time of the flowering of the plant, and of the ripening 

 of the fruit, showing that vegetables are susceptible to, and 

 much affected by, the stimulus of heat, and forming what bo- 

 tanists have been pleased to denominate the Calendarium 

 Florce. 



To account for these phaenomena, Darwin claims for vege- 

 tables the faculty of sensation, and gratuitously assigns to 

 them a sensorium, or union of nerves residing in each budf. 

 We may fairly contend, however, that the mere susceptibility 

 of the vegetable to the stimulus of light and heat is no proof 

 of its being endowed with the faculty of sensation ; because 



• n»j/ *wT6/» 'IffToj. Aldi, 106. -f- Zoon, vol. i. Sect. 13. 



even 



