The Cause of the Excretion of Wafer on the Surface of Nectaries. 15 



The phenomcnon which occurs under the name of honey-dew*) 

 (vvhen not connected witli insecls) very likely owes ils orit^in to a process 

 more or less closely related to the excretion of nectar. 



The sniall (h'ops of water which are loimd on the niyceiium of Piloh- 

 olus crystallinus '-) and which have been supposed lo originate from internal 

 pressure, are in all probability the result of osmotic action on the surface of 

 the same. 



If the delicate plants are allowed to stand for a short tinie in a dry 

 atmosphere, the drops vanish and in the place of each will be found a group 

 of radiating crystals, easily seen with the naked eye. If the same plant be 

 now covered with a bell-jar niany of the drops of water will reappear, and 

 precisely in those places where the crystalls were. 



If howewer the mycelium, instead of being subjected to a dry air, be 

 very carefully washed with the most delicate brush and distilled water, 

 and then placed in meist air under a ])oll-jar the drops will not as a rule 

 quickly reappear; often not at all. 



Placing very minute particles of sugar on the washed mycelium 

 quickly produced large drops. 



In a number of cases I have observed the appearance of drops on my- 

 celium which where not turgescent, and therefore not in a condition lo 

 exert any internal pressure. 



Resiilts. 



I. The excretion of nectar is caused by the osmotic action of a fluid on the surface of 



the nectary. * 



II. This has its proof in the fact that the excretion is wholly under the control of ex- 

 ternal manipulation. 



III. The excretion on the surface of nectaries can be wholly stopped by washing this 

 fluid away with water. 



IV. Nectaries made inactive through the Vemoval of this fluid by washing, can again 

 be brought into a State of activity upon the application of a sohition of similar 

 osmotic character (sugar-solution). 



V. The excretion of nectar may take place when the tissues of the plant are not tur- 

 gescent. 

 VI. The excretion of nectar is only very indirectly effected by positive or negative 



pressure. 

 Vit. The nectaries of many plants secrete equally well in light or in darkness, while 



those of others require either the direct suniight or strong diffused light. 

 VIII. The method of excreting in the nectaries is analogous to that of the glandulär 

 hairs on may plants. 



1) ÜNGEit, Beiträge zur Physiologie der Pflanzen. Sitzungsberichte der Mathem.- 

 Naturw. Classe der Kais. Akademie der Wissenschaften. Bd. XXV. Julihefte 1857. p. 450. 



2) Sachs, Experimental-Physiologie. 1865. p. 237. 



