The Cause of the Excretion of Water on the Surface of Nectaries. 7 



lila takes place which is again burst by a further metamorphosis of the 

 cell-wall. 



After the nectaries of Prunus lauroccrasus had excreted constantly for 

 seven or eight days the nectar still conlained lai'tic quanlities of sugar. 



I found in many cases that nectaries which had been active for a 

 number of days, from 12 to 20, lost many of their central parenchyma 

 cells, the walls completely disapparing; and that often an opening to the 

 surface of the nectary in one or more places was effected through the dis- 

 organization of the epidermis cells. Many of the remaining cells gradually 

 became thin-walled. There can be little doubt höre but that the tissue of the 

 nectary was changed into sugar. This whole process is closely related to the 

 niovements from place to ])lace of the nourishing materials, and of the 

 chemical changes which take pla<;e in the same. 



It may seem to those who are unfamiliar with the most recent investi- 

 gations in Osmose, that the slight dilferences which often exist betwecn the 

 concentration of the (luids within the plant and those on the surface of the 

 nectaries may be insufficient to cause any especial osmotic action. In the 

 investigations of Professor Pfeffer, whose work I have previously clted, a 

 1,0 ^ Solution of cane sugar exerted a pumping-force equal to a column 

 of quicksilver 57,1 Ctm. high. A 1,0 ^ Solution of saltpetre gave a column 

 of 175,8 Ctm., and the same concentration of sulphate of potassium a very 

 much higher column. These results were obtained with an artificial meni- 

 brane and serve to show the osmotic power of weak Solutions, 



The nectars of most plants taste sweeter and appear to contain more 

 organic substance than that of Frilillaria imperialis. From a careful an- 

 alysis of the nectar taken from the flowers of this plant I found 3,8 ^ solid 

 substance. The ash was almost inappreciable. The solid substance was 

 probably nearly all sugar. 



Unger ^) gives the specific gravity of nectars taken from three species 

 of Agave as follows : 



Agave Americana 1,05 

 geminiflora 1,09 

 lurida 1,20. 



Assuming that the solid substance in these nectars consists of cane- 

 sugar we shall have the following per cts. : 



For Agave Americana 10^ 

 geminiflora 1 8 ^ 

 - lurida 41,66^. 



Unger also gives the per cts. of sugar contained in the sap of several 



i) ÜNGER, Beiträge zur Physiologie der Pflanzen. Sitzungsberichte der Mathem.- 

 ISaturw. Classe der Kais. Academie der Wissenschaften. Bd. XXV. Juliheft 1857. p.446. 



