ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 273 



apparent in several species of Funhia and of HemerocalUs, as well as 

 in Dictamniis Fraxinella, Agapantlms umhellatus, &c. 



Experiment shows that the movements are determined by gravi- 

 tation, and are not purely spontaneous. The summit of the organ 

 tends in reality to turn from the earth. On counteracting the action of 

 gravity, by fixing the flower on a slowly rotating horizontal axis, the 

 curvature is prevented. In the same way, if the flower be turned 

 round, the plane of curvature always remains vertical, and has no 

 morphological relation to the position of the j)etals. The pistil of 

 Fraxinella, moreover, presents the curious property of being first 

 attracted by the earth, then two days afterwards repelled. In Scrophu- 

 laria nodosa, the peculiar curvature of the style towards the close 

 of the period of flowering seems, on the contrary, of a spontaneous 

 nature, as it takes place when gravity is counteracted. 



Nyctitropic Movements of Leaves.* — E. Mer gives the following 

 results from observations on the nocturnal position of the leaves in 

 Bobinia pseudacacia, Trifolium repens, T. pratense, Phaseolus vulgaris, 

 and Oxalis Acetosella. 



The movements of irritation and the nocturnal position of leaves 

 depend on an antagonism between the upper and under side of the 

 pulvinus of the leaf. This antagonism is due to the unequal tension 

 of the two sides caused by the absorption or loss of water. The 

 nocturnal position is independent of transpiration and of assimilation. 

 Any rapid change in the external conditions causes more or less 

 extensive and rapid movements of the leaf. The nocturnal position 

 appears to be the result of an action of irritation resulting from the 

 alternation of day and night, which has become more regular and 

 certain from hereditary habit and the inductive action of light. 



Mechanical Explanation of Spontaneous Nutations.t — J. Wiesner 

 gives further illustrations — taken from the phenomena of growth of 

 the epicotyledonary segment of Phaseolus multiflorus — in favour of 

 his theory that the hyponasty and epinasty of many organs are but 

 special cases of undulating nutation. In leaves cind stems hyponastic 

 curvature is the result of the unilateral development of the organ. 

 Epinasty, on the other hand, owes its origin to many different causes ; 

 in some cases partly or entirely to the greater resistance which the 

 under side of the organ opposes to the effort to bend dovrawards. 

 Epinasty shares with many other biological phenomena the pecu- 

 liarity of giving the impression of a simple phenomenon, while its 

 origin may really be very various. 



Secondary Geotropic Phenomena-f — J. Wortmann describes an 

 apparatus by which he has experimented on the effect produced on 

 geotropic curvatures of plant by alterations in the pressure and in the 

 constitution of the atmosphere. In very rarefied air the geotropic 

 curvatures continued, though with diminished intensity. If, on the 

 contrary, the whole of the oxygen is suddenly removed, all sensitive- 



* Bull. Soc. Bot. France, xxxi. (1884) pp. 213-23. 

 t Bot. Ztg., xlii. (1884) pp. 657-64, 673-82, 689-93. 

 % Ibid., pp. 705-13 (1 tig.). 

 Ser. 2.— Vol. V. T 



