OF THE EIGHTEENTH CENTURY. 243 
an inconclusive experiment bearing on this point. He says 
that seedlings, over which a horizontal plate of an opaque 
material is suspended, do not grow straight upwards, but 
curve outwards from the centre. He notes that, if the plate is 
made of glass, the seedlings grow vertically up until they nearly 
touchit. Butit is not clear that he recognised a heliotropic effect, 
since he seems to have expected to get different results by 
employing copper, porcelain, and cardboard as his opaque 
material. Hope made this experiment (J7S. Lectures, p. 94) and 
illustrates his method in Fig. 12 on the plate following p. 102. 
He clearly understood that the outward curvature of plants 
shaded by a piece of board is an effect of light, for he gives other 
experiments to settle the question whether such movements are 
“to get at the light or the air,’ and decides in favour of light. 
Another set of excellent experiments directed to the same 
point are illustrated in his diagrams. 
Fig. 4, Plate xlv.. shows Asperula odorata curving upwards 
“in the open air,” ze, probably when lighted from above. 
In Fig. 5, Plate xlv., the same plant shows apogeotropism 
when but faintly lighted from below.! 
Fig. 6, Plate xlvi., shows that when the plant is well 
illuminated from below by means of a mirror, the geotropic curve 
is straightened out by the stimulus of light. 
Fig. 7, Plate xlvi., shows another method for demonstrating 
the victory of heliotropism. 
These experiments were made in June 1780, but the facts 
were not known to physiologists until nearly 100 years later, 
when H. Miiller Thurgau? and Elfving® published them. 
It is true that in 1833 Schultz Schultzenstein‘ says that “seeds of 
Brassica oleracea, Sinapis alba, and Phaseolus vulgaris placed in 
moss and arranged so that they receive the sun’s rays by means 
t [t is not certain that the curve shown in Fig. 5 was produced under these 
conditions. Probably it is meant to show that the curvature obtained in Fig. 4 
remains under the conditions of Fig. 5. 
* ony 1876, p. 94. 
® Acta Soc. Sc. Fennice, T. xii, 1883, p. 25: Elfving’s paper is, however, dated 
1880. The experiment is iacladed in F, Darwin and Acton, Practical Physiology, 
ed. iii, p. 182. 
* See ‘‘ Rapport sur le grand prix de physique” in the Archives de Botanique ii., 
p- 431. The author’s name is here given as Schultz, but from the nature of the 
Rapport it is clear that he is the Schultz Schultzenstein celebrated for his uncon- 
vincing work on latex, 
