56 
y. B Fanner . 
ON THE MECHANISM WHICH IS 
CONCERNED IN EFFECTING THE OPENING AND 
CLOSING OF TULIP FLOWERS. 
By J. Bretland Farmer, F.R.S., 
Professor of Botany in the Royal College of Science, London. 
T is a well-known fact that the flowers of the Tulip, in common 
with those of many other plants, are able to open or close 
according to the circumstances in which they happen to be situated. 
Thus when brought from a cold into a warm room the closed 
flowers will speedily expand, hut will again close on renewed 
exposure to cold air. 
It has been said that these movements of the perianth leaves 
(which for the sake of brevity may be termed petals) of the Tulip 
are due to the prevalence of epinastic and hyponastic conditions of 
growth, and that in this way the opening and closing respectively of 
the flowers are to be explained. It is perfectly true that Tulip 
flowers normally continue to grow for a considerable time after, 
they may have first expanded, but it does not necessarily follow 
that this fact is to be in any way directly connected with the 
movements in question. It may indeed be reasonably doubted 
whether the rate of growth is sufficiently rapid to account for the 
alteration, especially in the case of that consequent on lowering 
the temperature. 
The phenomena might, on the contrary, be referable to the 
agency of a localised irritable tissue situated towards the outer or 
inner face of the petals. If the cells of such a tissue were capable, 
on appropriate stimulation, of altering their size or shape to an 
extent greater or less than are the cells of the adjacent tissues 
under similar circumstances, opening and closing movements would 
certainly occur. Such a mechanism might justly be compared to 
that which effects the corresponding changes in the positions of the 
leaf-lobes in Dionaea. In this plant, as is well known, the 
movements depend immediately on a difference in their relation to 
water existing between the cells of the upper and lower surfaces 
respectively. The former on stimulation readily part with water, 
and hence the still turgid cells at the lower surface then cause a 
closure of the lobes. In the quiescent expanded condition this 
turgor of the lower cells is balanced by that of the upper cells, and 
the lobes are thus forced to diverge from each other. 
