ABSORPTION AND TRANSMISSION OF WATER 99 



the high osmotic pressure caused by evaporation will fully 

 account for the outward passage of water which keeps the 

 nectar of flowers and leaves in the liquid condition on the 

 dryest days. Nectaries may even be artificially formed in this 

 way ; if minute granules of sugar are placed upon the hyphse 

 of Mucor, droplets of water will soon form and increase in size 

 until they run down and fall off. The same may be done 

 with leaves ; a small mass of sugar upon the epidermis will 

 soon extract enough water osmotically to make a large drop- 

 let. The method of extraction of the water in these arti- 

 ficial cases is clear enough after a small portion of the sugar 

 has been put into solution. Water to form the first minute 

 amount of solution cannot be withdrawn from the leaf- 

 cells by osmotic action. But all cellulose membranes, even 

 cuticularized ones, are more or less saturated with water of 

 imbibition. Now, the sugar particles resting upon the leaf 

 come in contact with these moist membranes and immedi- 

 ately begin to dissolve in the water therein imbibed. After 

 the start is once made, be it ever so infinitesimal, osmotic 

 action will accomplish the outward flow of water from the 

 comparatively weak solution within the cells to the saturated 

 one on the surface. 



But in the case of the natural nectary the original exuda- 

 tion of the sugar-containing sap has not yet been accounted 

 for. Perhaps this can be explained in a manner parallel to 

 that just postulated for the case of the water pore. At a 

 certain stage in its development the glandular tissue of the nec- 

 tary may undergo a change such that, through a rapid increase 

 in soluble content, the osmotic pressure of the sap of its 

 component cells rises suddenly. This rise in turgor pres- 

 sure may act as a stimulus upon the protoplasm, and the latter 

 may, in turn, respond by a change in its structure, so that it 

 becomes permeable to solutes as well as water. If this be 

 true, the contraction of the stretched cellulose walls must 



