258 BOTANICAL GAZETTE [april 



attributed to the diminished pressure, but this explanation would 

 not account of course for the similar increase at high latitudes. 



In investigating experimentally the influence of pressure, I 

 covered the plant under experiment with a tabulated bell jar waxed 

 to fit tightly to a ground glass plate and connected by means of a 

 stopcock with the water aspirator. A similar plant was placed * 



under a control bell jar. In some of the experiments air was daily 

 renewed in both low pressure and control jar; in others its con- 

 tinual renewal was provided for by admitting a current of air which 

 bubbled through water, and in the case of the low pressure jar 

 entered by means of a capillary tube with a very small aperture. 

 This latter method is similar to one employed by Schaible (22). 

 By the use of an aneroid barometer the pressure was maintained at 

 about 50 cm., or two-thirds atmospheric pressure, the prevailing 

 condition at altitudes of about 10,000 ft. Repeated investigations 

 were made with the following plants: for guttation, Tropaeolum 

 majus and Avena saliva; for nectar secretion, Tropaeolum majus, 

 Impatiens Sultani, A but Hon striatum, Euphorbia pulcherrima, Canna 

 indica y Fagopyntm esculentum, Salvia splendens, Coleus Blumei, 

 Antirrhinum majus, and Prunus americana. 



There were no constant differences in secretion which could be 

 detected by either physical or chemical means. It is very doubtful, 



mea 



which 

 It is a 



more 



warmth 



periods favoring activity. Hence it seems very probable that any 

 relation between atmospheric pressure and honey flow is to be 

 attributed to the bees and not to the plants. 



LIGHT 



Haupt 



the extrafloral nectaries of several species of Vicia are stimulated 

 to activity by light. The first author adds Lobelia erinus and the 

 last the Euphorbiaceae as plants that require the light stimulus 



■ 



for secretion. The two latter authors, however, state that in the 

 greater majority of cases secretion is only indirectly related to 



