THE NATURAL HISTORY OF THE FLOWER. 297 
leave it undecided whether light or temperature be the main 
factor; the latter: seem to point to reduced light as the main 
cause of reduction of the corolla. This has been in a large 
measure proved by the recent experiments of Vichting *, upon 
the action of light of various degrees of intensity upon the 
flowers of plants which had a tendency to cleistogamy. At the 
same time, this does not seem to explain everything ; for instance, 
the fact observed many times on Salvia, that normal flowers and 
cleistogamic flowers occur side by side at the same node, This 
phenomenon the author is inclined to regard as an effect of 
varying temperature: the flowers had not usually opened 
simultaneously, and so had been exposed to different conditions 
of temperature at corresponding periods of growth. This would 
cause in them varying degrees of protandry (according to the 
hypothesis of the origin of dichogamy proposed by Meehan and 
adopted by the writert). Those that were thus caused to 
become very protandrous would be fertilized in the bud, and the 
corolla would probably wither without ever opening. A slightly 
less degree of protandry would give the type of fig. 24 and a 
lesser still would give the normal flower. This reasoning of 
course is not conclusive, as it may be applied to the action of 
light instead of heat ; but we have a certain amount of evidence 
in favour of the view that dichogamy is dependent on temperature, 
and it therefore does not seem a very forced view, especially as 
the temperature conditions are perhaps more variable than those 
of light during a short period. 
Viola tricolor, Linn.—Véchting’s experiments bring out, among 
other interesting facts, that in a zy gomorphie flower the upper 
lip becomes reduced, under the action of diminished light, more 
rapidly than the lower. Some specimens of Viola tricolor, var. 
arvensis, gathered on Dee. 9, 1893, illustrate this reduction very 
well. The whole corolla is small in comparison with the calyx, 
but the upper lip is far more reduced than the lower (fig. 26). 
Finally, the author wishes to thank Messrs. F’. Darwin, R. I. 
Lynch, and I. H. Burkill for much valuable advice and assistance 
kindly rendered. 
* “Ueber den Einfluss d. Lichts auf die Gestaltung und Anlage der Blithen.”’ 
Pringsheim’s Jahrb. xxv. 1893, pp. 149-208. 7 
+t “On Gynodiecism, with a preliminary note on the origin of this and 
Similar phenomena.” Proc. Camb. Phil. Soe. viii. 1893, pt. iii, 
LINN. JOURN.—BOTANY, VOL. XXX. YX 
