14 W. P. Wilson. 



possible conclusion was that the neclar had been absorbed ') . I have re- 

 peated this several limes wilh the same result. If one places a thin section 

 of living plant tissue in a concentrated Solution of sugar-sirup and ob- 

 serves the same under the microscope it will be seen that the Solution 

 passes readily through the cell-walls, acts osmotically on the plasma-mem- 

 brane withdrawing some of the water which the eells contain and causing 

 a inore or less rapid shrinking or contraction of this living membrane. It 

 cannot be readily shown that any of the sugar passes through the plasma- 

 membrane, but that the cell-walls oflier no obstruction is evident. In the 

 absorption of nectar it is easily conceivable that the sugar is taken up 

 through imbibition by the cell-walls. Whether the sugar passes again into 

 the cell, and if so in what combination must be further studied before any- 

 thing definite can be said. The nectar on the surface of the nectaries of 

 Prunus laurocerasus was removed with a pipette every day for eight suc- 

 cessive days. On the eighth day the nectar appeared to be as rieh in sugar 

 (Fehlings test) as on the first, showing that there was a constant supply of 

 the same^). 



The appearance of sugar on the surface of the nectary as well as its 

 disappearance into the cell-walls is bound up with chemical changes and 

 with the transport of nutritive and olher materials in the plant. The whole 

 subject needs further investigation. 



General Conclusions. 



In the case of the glandulär hairs found on so many plants we have 

 secretory organs wholly analogous to the nectaries, in so far as the method 

 of secretion is concerned. There are nectaries also in which the secreting 

 surface is made up of glandulär hairs. This is the case with Vicia faba. 



The secretion on the leaves of Dionaea results from an external irrita- 

 tion caused by the presence of a nitrogenous substance. 



The direct excretion of the fluid on the surface of the leaves is prob- 

 ably caused by an active one-sided pressure in the underlying paren- 

 chyma cells. 



Tbe excretion in the case of Drosera may be more or less influenced in 

 the same way by nitrogenous substances, and also in addition be partially 

 caused by osmotic action. The excretion of water in the pitchers of Nepen- 

 thes and Sarracenia, and on the leaves of Pinguicula requires further study. 



1) BoNNiER, Les Nectaires. Etüde critique, anatomique et physiologlque. Annales 

 des Sciences naturelles — Botanique — VI Series. Tome VIII. 1879. — The views put 

 forth by Bonnier with reference to the absorption of Nectar seem to me to be erro- 

 iieous. 



2) I have already described the metamorphosis of the parenchyma and parts of the 

 epidermis into sugar which I observed in these nectaries. 



