10 W. P. Wilson. 



iness inlo the lissues of the nectary. The smallness of the cells, favoring 

 a high pressure, and the almost total failure of intercellular Spaces will, in 

 a measure, account for this. 



As still further illustrating this principle I selected three branches 

 from Prunus laurocerasus, as nearly equal in age and appearance as pos- 

 sible, and placed them under a bell-jar until all the nectaries were active. 

 I now subjected one of the branches to a pressure equal to a column of 

 mercury 25 ctm. in height, another to a negative pressure of 15 ctm., and 

 the third I placed in a glass of water. The three branches were now 

 covered by one and the sanie bell-jar. 



The amount of nectar excreted was carefully observed. If there was 

 a difference, which is quite probable, it was so slight that it was impos- 

 sible to observe it without more accurate methods of measurement, than 

 were applied. The surface of an actively secreting nectary generally differs 

 from other surface parls of the leaf in being devoid of cuticula. Other Ihings 

 being equal, this should allow a more ready exit of water under pressure, 



A pressure of 20 or 25 ctm. quicksilver is sufficient to inject the 

 leaves, but may be less by an atmosphere than that existing in the small- 

 celled tissue of the nectary. 



The excretion of nectar in the case of Prunus laurocerasus has been 

 shown not to be in direcl relation to the water supply of the plant. The 

 beginning of the excretion however, i. e. the metamorphosis of the cell- 

 wall and the raising and final bursting of the cuticula, shows a much closer 

 counection with the same. 



Six branches from Prunus laurocerasus, all with inactive nectaries, 

 as near alike in age and appearance as it was possible to select, were cut 

 from the Iree and placed under the following conditions : 



No. 1, Subjected to a pressure of 20 ctm. quicksilver. 



No. 2, Subjected to a pressure of 10 ctm. quicksilver. 



No. 3. Placed in a glass of water. 



No. 4. Subjected to a negative pressure of 10 ctm. quicksilver. 



No. 5. End of the brauch wrapped in bibulous paper, a strip of which 

 hung down into waler below. 



No. 6. Placed in a glass without water. All the branches were cov- 

 ered with bell-jars and kept in a very meist atmosphere. 



The nectaries on brauch No. 1 began to excrete first after 24 hours, 

 those on No. 2, 12 hours later, No. 3 about 13 hours after No. 2, No. 4 a 

 few hours after No. 3, No. 5 were much slower, and only four nectaries 

 had begun to secrete on the seventh day. 



Some of the nectaries of No. 6 became meist but no further change 

 took place and the branches gradually withercd. The amount of moisture 



