208 PHYSIOLOGY OF NUTRITION. 



escape of fluid from plant structures. This is the case, e.g., in 

 many nectaries, 2 and we select for examination those of Fritillaria 

 imperialis. At the base of the perianth leaves in the flower of 

 Fritillaria, are easily seen comparatively large bowl-shaped nec- 

 taries. There is present in them a sugary sap, containing glucose. 

 This we can easily ascertain by rinsing the base of a few perianth 

 leaves with a little water, and pouring the fluid obtained into 

 boiling Fehling's solution. We further very carefully and re- 

 peatedly rinse the nectaries of several perianth leaves with water, 

 dry them with blotting-paper, and then put a bell-glass over them. 

 In the nectaries of a few of the perianth leaves we now place a 

 granule of moistened sugar, reserving the others for comparison. 

 After a few hours the former again contain a sugary sap, while 

 the latter remain dry. The sugar attracts water to itself, by 

 osmosis, from the cells of the nectary, without pressures being 

 thereby set up ; and what is effected in the experiment by the 

 sugar added, is probably effected under normal conditions by 

 osmotically active bodies produced by the metamorphosis of the 

 substance of the outer membranes of the epidermal cells of the 

 nectaries. 



When felled tree trunks, rich in sap, are exposed to the sun's rays, 

 it frequently happens that fluid exudes from their cut surfaces, 

 and this arises from the fact that the air within the wood elements 

 has expanded owing to rise of temperature, and driven out the 

 water also present in the structures. The following experiments 

 give us further information. Pieces 20-25 cm. long and 3-5 cm. 

 thick are cut in cold but damp weather, in winter, from boughs of 

 willow, elm, ash, hazel or Pavia rubra, which last I chiefly used 

 in my experiments, and, after their ends have been very carefully 

 smoothed, are laid for about twenty-four hours in water at a tem- 

 perature of about 2 C., so as to increase the quantity of water 

 within them. We then put them in a cylinder containing water at 

 25-30 C., with their upper ends projecting slightly above the 

 surface. A fairly large quantity of water soon collects on the 

 smooth cut surface on the top of each. I also observed a similar 

 escape of water, resulting from expansion of the air present in 

 the wood elements, when pieces 15 cm. long and 2 cm. thick, cut 

 in winter from branches of Abies pectinata, were placed in water 

 at a temperature of 24 C. When they were subsequently placed 

 in water at 5C., the water which had issued from the cut sur- 



