198 PHILOSOPHICAL TRANSACTIONS. [aNNO 1758. 



find that heat and cold were n(jt 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 illus- 

 trious Swede ; and the naturalist is greatly indebted to him for so far extending 

 his observations on it. 



The subject of the somnus plantarum cannot but be highly entertaining to the 

 lovers of natural knowledge : and such, I apprehend, cannot be less entertained 

 with that faculty which Linneus calls vigiliae 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 situa- 

 tion 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 sub- 

 ject of these observations, which observe a more constant and uniform law in 

 this particular. These open and shut duly and constantly at certain and deter- 

 minate hours, exclusive of any manifest changes in the atmosphere; anrl this 

 with so little variation in point of time, as to render the phenomenon well worth 

 the observation of all whose taste leads them this way. This faculty in the 

 flowers of plants is not altogether a new discovery : but we are indebted to the 

 same hand for additional observations on this head also. It is so manifest in one 

 of our common English plants, the tragopogon luteum, that our country-people 

 long since called it John-go-to-bed-at-noon. Linneus's observations have ex- 

 tended to near 50 species, which are subject to this law. What we find princi- 

 pally on this subject, is in the Philosophia Botanica, p. 273. We will enumerate 

 these plants, and mention the time when the flowers open and shut, that those 

 who have opportunity and inclination may gratify themselves, and probably at 

 the same time extend this branch of botanic knowledge still further. 



It is proper to observe, that as these observations were made by Linneus in the 

 academical garden at Upsal, whoever repeats them in this country will very pro- 

 bably find, that the difference of climate will occasion a variation in point of 

 time : at least this will obtain in some species, as our own observations have 

 taught us ; in others the time has corresponded very exactly with the account he 

 has given us. Whether this faculty has any connexion with the great article of 

 fecundation in the economy of flowers, Mr. P. cannot determine: in the mean 

 time it is not improbable. Future and repeated observations, and well-adapted 

 experiments, will tend to illustrate this matter, and it may lead the way to a full 

 explanation of the cause. 



1. Aiiagallis flore phoeniceo c. B. pin. 252. Raii Syn. p. 282. Anagallis ar- 



