The Cause of the Excretion of Water on the Surface of Nectaries. 1 1 



supplied, Ihus seems to have a comparatively direct influence on the pro- 

 duclion of Ihe fluid on the surface of the neetary. 



I have observed Ihat the nectaries on plants of Vicia faba and Acacia 

 lophanta growing in pots are prevented from excreling when kept sonie- 

 what drier than Ihe natural condilion. 



Influence of Temperature on the Excretion of Nectar. 



The influence of temperature within cerlain limits on the excretion of 

 nectar, after the nectaries have begun to be active, is not very striking. 



If we select six potatoes, cut ofl" their opposites ends, on one end of 

 each make a round smooth hole 1 ctni. deep and Ys ctni. in diameter, place 

 these in two plates three in each wilh a little water, supply all the six holes 

 by means of a pipetle with two small drops of a 20 % sugar Solution, place 

 one plate in a room having a temperature of 20"C. and the other in a 

 room with a temperature of 1 ° C. we shall be provided with the means in 

 these artificial nectaries of observing the influence of temperature on os- 

 motic actioni). If the sinking of the temperature is sufficient to produce 

 enlargement of the minute Spaces between the particles making up the 

 plasma-membrane, thus allowing the Solution in the cells through exosmose 

 to pass out, we may have a lessening of the activity ; otherwise not. The 

 holes made in the potatoes will in both rooms in a few hours be filled with 

 fluid, pumped up from the underlying tissues. There will be very little 

 observable difference in favor of the warm room. 



Brauches of Prunus laurocerasus changed from a temperature of 18" 

 to 20° C, under the influence of which the nectaries were very active, to 

 a temperature of from i ° to 5° C. continued to excrete nectar for several 

 days only a little less in amount than in the warm room. Vicia faba and 

 Acacia lophanta were subjected to the same changes of temperature, and in 

 the main, with similar results. 



In so far as temperature is concerned, a complete analogy seems to 

 exist between the action of these artificial nectaries, from potatoes, and of 

 the real nectaries of plants. In Professor Pfeffer's critical study of Osmose, 

 already cited, it has been shown that the pressure which any given Solution 

 and membrane are capable of generating is not influenced to any great 

 extent by a change of from 15° to 20° G. The membranes used are not 

 wholly analogous to the plasma-membrane which lines the cell-walls. 



Brauches of Prunus laurocerasus placed at once in a cold room before 

 the nectaries had begun to excrete remained in a temperature for 13 days 

 ranging from 2,5° — 7°C. The nectaries showed no signs of excretion. 



1) The plate and potatoes used to test the low temperature should be placed several 

 hours before use in the cold room, that the proper temperature at the beginning of the 

 experiment may be secured. 



