362 PHYTOLOGY. 



the petioles, and also of the folioles, and put them into a phial of 

 water, No. 1. 



I took as much in quantity of the inactive part of the petioles and put 

 them into another phial with the same quantity of water, No. 2, and 

 sunk them both into the tan in a hothouse. When they had stood thirty- 

 six hours, I smelt them both, and found that phial No. 1 had a pretty 

 strong sickish or faintish smell, but that of the other was hardly per- 

 ceivable. When they had stood forty-eight hours, I found the smell of 

 the first increased, but not that of the second. I took some of the 

 water of the first, and put to it the syrup of violets, and it turned it of 

 a very fine green ; No. 2 had no effect upon the syrup. It did not pro- 

 duce the same effects again, and I continued them in it for more than 

 three weeks, upon the very same parts, and at last they both produced 

 an acid. 



The St. John's Wort opens its flower when it is dark, never when it 

 is light ; but they never close again when it is light, as do the Con- 

 volvulus [Ipomcea boivx-nox Linn.], Evening Primrose [(Enoihera, several 

 species], &c. ; indeed, I believe its flower only lasts one night and one day. 



I have seen Honeysuckles which flowered in the night, two of them 

 before twelve o'clock at night. A Holyhock, whose flower was pro- 

 truding in the morning, opened in the forenoon. 



Of the Action of Light. — It was thought, from common observation, 

 that light was the immediate cause of the green colour of vegetables ; 

 but upon a further investigation of the subject, it appears to be only 

 the remote cause. That it is not an immediate cause in all cases is 

 plain, from vegetables of the same species not all being green ; nor green 

 in all parts of the same vegetable, as the Variegated Holly, Aloe, &c. 

 Besides, many vegetables are green through and through their whole sub- 

 stance, as the &c. ; [some mosses, lichens, confervae] 

 and many vegetables that are green on their outside, viz. in their cutis 

 and in their new layer of wood, especially when but newly formed, are 

 also green on the inner surface of the canal of the pith, as in the young 

 shoots of the Elder. Erom all which it would appear that fight is not 

 the immediate cause of the green colour, but a remote cause, viz. the 

 cause of a certain degree of health or proper action, which produces the 

 green colour ; and that those plants or parts which are not green, when 

 exposed to the light, are not capable of taking on this necessary mode 

 of action, although under the influence of light. In other words, the 

 light is capable of stimulating most plants to such action as produces a 

 green colour in certain parts of the plant, no matter whether imme- 

 diately, or not immediately, under the influence of light. 



The leaves of most plants are green, but not of all. In those that 



