The examples of sleeping plants instanced by Alpinus are but few. That author says, it was common to several Egyptian species[17]; but specifies only the Acaciæ, Abrus, Absus, Sesban, and the Tamarindtree. Cornutus some time afterwards remarked this property in the Pseudo-acacia Americana. From that time it has remained almost unnoticed, till Linnæus, ever attentive to nature’s works, discovered that the same affair was transacted in many other plants; and his observations have furnished us with numerous and obvious examples thereof. Mr. Miller mentions it in the _Medicago arborea Lin. Sp. Pl. 778_. and we may add to the list two other common plants not mentioned by Linnæus: these are the _Phaseolus vulgaris_, common kidney-bean; and the _Trifolium pratense purpureum majus_, or clover-grass: in both which this nocturnal change is remarkably displayed. Doubtless the same property exists in numberless other species; and future observation will very probably confirm Dr. Hill’s sentiment, that no “plant or tree is wholly unaffected by it.” It is now more than twenty years since Linnæus first attended to this quality in plants. In his _Flora Lapponica_, when speaking of the _Trifolium pratense album_, as above-mentioned, he remarks, that the leaves of the Mimosa, Cassia, Bauhinia, Parkinsonia, Guilandina, and others in affinity with them, were subject to this change in the night time: and he had then carried his observations so far, as to find, that heat and cold were not the cause of this quality; since they were alike influenced by it when placed in stoves, where the temperature of the air was always the same. The merit of reviving this subject is therefore due to the illustrious Swede; and the naturalist is greatly indebted to him for so far extending his observations thereon. The subject of the _somnus plantarum_ cannot but be highly entertaining to the lovers of natural knowlege: and such, I apprehend, cannot be less entertained with that faculty, which Linnæus calls _vigiliæ florum_; of which we shall give a brief account. Previous to our explanation of this affair it is proper to observe, that the flowers of most plants, after they are once opened, continue so night and day, until they drop off, or die away. Several others, which shut in the night-time, open in the morning either sooner or later, according to their respective situation in the sun or shade, or as they are influenced by the manifest changes of the atmosphere. There are however another class of flowers, which make the subject of these observations, which observe a more constant and uniform law in this particular. These open and shut duly and constantly at certain and determinate hours, exclusive of any manifest changes in the atmosphere; and this with so little variation in point of time, as to render the phænomenon well worth the observation of all, whose taste leads them this way.