The Cause of the Excretion of Water on the Surface of Nectaries. 3 



The parenchyma of the nectary, the group of cells which seems to be ac- 

 tively concerned in Ihe secrelion, is almost invarial)Iy made up of smaller 

 cells Ihan ihat of the tissue immedialely Surround ing it. 



The intercellular spaces are either entirch wanling or very small. 

 The form and color of the Contents of Ihis group of cells is also generally 

 very niarked. Various proporlions of glucose with nitrogenous Compounds 

 are easily shown to e.vist under the microscope ') . It is easy to prove the ex- 

 istence of large quantilies of grape sugar^) in the parenchyma cells of the 

 nectaries on the leaves tff Prunus laurocerasus. Sugar, or starch, or both 

 are invariably present in more or less varying quantilies. 



The fluid called neclar, excreted from the surface of the nectaries is 

 usually sweet'to the taste and contains in nearly all cases a large per cent. 

 of solid substance, the larger proportion of which is sugar. 



The question which I shall attempt to answer is, how this fluid or 

 nectar finds its way to the surface of the nectary? 



We may at once exclude the so called root-pressure from consideration 

 since Unger^) as long ago as 1844 discovered that the nectaries on the 

 leaves of Acacia lophantha continued to excrete after being severed from 

 the parent plants ; and as it is a well known fact that the nectaries in the 

 flowers of Fritillaria Imperialist) and many others secrete nectar after 

 having been cut and placed with their stems in water. 



There are however but two ways possible for this excretion to take 

 place. Either the nectar is forced to the surface by means of active internal 

 pressure, which is the view entertained by botanists at the present time, 

 or it takes its place there as the result of osmotic aclion exerted by a fluid 

 on the surface of the nectary. 



The following considerations and experiments will offer the means 

 of deciding the question. 



If there be placed on the surface of an animal membrane distended 

 with water, and surrounded with a saturated atmosphere, a particle of 

 moistened sugar, or a drop from a Solution of the same, a current of water 

 will be at once generated, flowing from the interior to the exterior of the 

 membrane. 



This current takes place according to the well known laws of Osmose 

 and needs here no explanation. 



If branches from Buxus sempervirens, Hex and Ficus elastica^) be cut 

 and placed in dishes containing water^ and on the surfaces of some of the 

 leaves of each, be placed small drops of a Solution of sugar, salt, or gum- 



1) Behrens, Die Nectarien der Blüthen. Flora 1879. p. 2. 



2) For method of proof see: Pringsheims Jahrb. VIH. p. .'iSS. 1872. 



3) Unger, Flora 1844. p. 707. 



4) Sachs, Physiologie der Pflanzen. 1865. p. 236. 



5) Leaves from Ihese plants have no storaata on their upper surfaces. 



