3-6 ANNUAL OF SCIENTIFIC DISCOVERY. 



they had been exposed to the open air, and before they were directly illumi- 

 nated by the lunar rays. He thus avoided any causes of error which might 

 have arisen from the imperceptible motion of the air, or from a slight change 

 of temperature ; and he satisfied himself fully that the effects observed did 

 result entirely from the action cf tLc rn} s oi' light from the moon. Without 

 entering into minute details, it is sufficient to say that the results were ascer- 

 tained when the temperatureof the air was 70 Fahr. ; and when Saussure's 

 hygrometer indicated a medium state of humidity. Under such conditions, 

 the leaf stalks of Mimosa ciliata were raised hah" a centimetre, or about four- 

 tenths of an inch ; those of the Mimosa pudica were raised one inch and two- 

 tenths ; whilst the leaflets of Desmodium gy rains exhibited distinct vibrations. 

 It was thus demonstrated that moonlight has the power per se of awakening 

 the Sensitive Plant, and consequently that it possesses an influence of some 

 kind on vegetation. It is true that the influence was very feeble, compared 

 with that of the sun ; but the action, such as it is, is left beyond further ques- 

 tion. This being so, the question remains, what is the practical value of the 

 fact? It will immediately occur to the reader that possibly the screens which 

 are drawn down over hothouses at night, to prevent loss of heat by radiation, 

 may produce some unappreciated injury by cutting off the rays of the moon, 

 which Nature intended to fall upon plants as much as the rays of the sun. 



" Even artificial light is not wholly powerless. De Candolle succeeded in 

 making Crocuses expand by lamp-light, and Dr. Winn, of Truro, has suggested 

 that the oxyhydrogen lamp may be made subservient to horticulture in the 

 long dark days of winter. It does not, however, appear that this hypothesis 

 rests upon any experimental basis." 



OX THE LAW OF PHYLLOTAXIS. 



The following is an abstract of a paper on the above subject, read at the 

 last meeting of the American Association, by Dr. T. C. Hilgard: 



He wished to present an attempt towards constructing an organic law of 

 Phyllotaxis, towards constructing a theory of the cause of the arrangement 

 of leaves. It was well known to the gentlemen that hitherto phyllotaxis, or 

 the arrangement of leaves, had only been studied in its mathematical relations, 

 and in its analogy to cosmical or to zoological order. It had been shown 

 that leaves not opposite are arranged about a stem always in either two, 

 three, five, eight, or thirteen rows, and that if the bases of the leaves taken 

 in their order of height on the stem be connected by a thread winding round 

 the stem, then between any two successive leaves in a row, the thread winds 

 round the stem once if the leaves are in two or three rows, twice if in five 

 rows, three times if in eight, five if in thirteen, &c. In other words, two 

 successive leaves on the thread will be at such a distance, that if there are 

 two rows, the second leaf will be half way round the stem ; if three rows, the 

 second leaf will be one third of the way round ; if five, the second will be 

 two-fifths of the way round ; if eight, three-eighths ; if thirteen, five-thir- 

 teenths, &c. But the question of Dr. Hilgard is, why is this so ? "What is 

 the organic law of development that produces this result ? If we cannot 

 answer this question, can we not at all events throw some light upon it, 



