144 Shaw—Structure of the Flowers in 
“Tn the late autumn and early spring, when it is cool, and 
there are no flower-seeking insects, the Dead-nettle is able to 
do without the luxury of corollas, which are the means of 
alluring insects, and as a fact only cleistogamous flowers 
make their appearance at those seasons. It must not, of 
course, be imagined that the plant exercises an intelligent 
discretion of its own when it abandons the development of 
corollas. The connection between this effect and the afore- 
said conditions is indirect, and we must conceive that the 
nature of the stimulus which results in the inception of 
flower-buds is different, when a plant is subject to the influence 
of the short days and the low temperature of late autumn and 
early spring, from what it is under the conditions prevailing 
‘on warm summer days.” 
Vochting! showed experimentally that the development of 
flower parts depended much on the presence of light: that if 
light were diminished the corolla suffered first and later the 
other floral members. In the case of Lenaria spuria he has 
also been able to produce either chasmogamic or cleistogamic 
flowers at will by regulating light intensity. Schively? found 
that chasmogamic flowers of Amphicarpea monotca never 
appeared in winter or spring on plants reared in the green- 
house. Only in summer were such produced, and this fact was 
attributed to the relatively low light intensity of winter. Lud- 
wig’ expresses the view that cleistogamy is caused by unfa- 
vorable weather or lack of insects at flowering time. Engler* 
states that amphicarpy in hermaphrodite flowers is always 
associated with cleistogamy. In commenting on the fact that 
where cleistogamic flowers are produced, seed often fails to 
mature from the chasmogamic ones, he makes the important 
1 Véchting. Einfluss des Lichtes. Prings. Jahr. xxv, 1893, p. 149. 
2Schively. Loc. cit. 
3Ludwig. Lehrbuch der Biologie der Pflanzen, p. 427. 
4Engler. Bot. Central, 95. Beih, p. 265. 
