144 Shaw — Structure of the Flowers in 



" In 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 

 licfht were diminished the corolla suffered first and later the 

 other floral members. In the case of Linaria 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 AmpJiicarpcea vwnoica 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 



^Vochting. Einfluss des Lichtes. Prings. Jahr. xxv, 1893, p. 149. 

 2Schively. Loc. cit. 



3Ludwig. Lehrbuch der Biologic der Pflanzen, p. 427. 

 *Engler. Bot. Central, '95. Beih, p. 265. 



