The Cause of the Excretion of Water on the Surface of Nectaries. 13 



fused light, begin to secrete again after a few hours when brought back 

 into the sunlight. 



Plants of Vicia faba were cullivated in small pots unlil Ihey were from 

 slx to Iwelve Clms. high. At this time they showed no signs of excreliug 

 nectar. They were then placed in bell-jars so arragned that the entering 

 air passed through a tube filled with small pieces of pumice-stone which 

 had been previonsly soaked in a Solution of caustic potash. By this means 

 the plants were allowed to continue their growth in an atniosphere entirely 

 free from carbonic aeid. When the bell-jars were placed in the direct sun- 

 light, the nectar was secreted as freely as though the plants had been 

 left in the open air. Whatever changes the light may cause in the contents 

 of the cells of the nectaries, or may exercise on the tissues of the same, 

 causing the excretion to take place, cerlain it is that these changes have 

 no direct relation to assimilation. 



According to Wunsciimann ') the secretion in the pitchers of Nepenthes 

 takes place with much more rapidity in the sunshine than in the shade. 



Darwin 2) has observed that the nectar in the flowers of Lobelia erinus 

 and on the nectaries of Vicia sativa is only secreted in the bright sunshine. 

 The excretion of nectar on most nectaries however is only very indirectly 

 under the influence of light. 



Absorption of Nectar. 



I have observed on the nectaries of Vicia faba large drops of nectar 

 which afterwards entirely disappeared, and under such conditions as to 

 leave it probable that evaporation was not the cause. 



In Order to determine whether the nectar under certain conditions 

 may be absorbed into the nectary I took fine plants in pots of Vicia faba 

 grown in the sun, whose nectaries were secreting actively and placed them 

 in diflFused light in the back of a room where my previous experience had 

 shown me that these plants would secrete no nectar on account of want of 

 light. Large drops were Standing on the nectaries. The plants were covered 

 with bell-jars and provided with an atmosphere saturated with moisture. 

 On the following day some of these nectaries showed no trace of nectar. 

 The nectaries were not even meist. On the third day still others were dry. 

 An examination with the lense showed no signs of any residue on the sur- 

 face of the nectaries. There could have been no evaporation, and the only 



i) Wunschmann, Über die Gattung Nepenthes, besonders in Rücksicht auf ihre phy- 

 siologische Eigenthümlichkeil. 1872. p. 38. 



2) Darwin, Die Wirkung der Kreuz- und Selbstbefruchtung im Pflanzenreich. 1877. 

 p. 388. 



