I5 6 PLANT PHYSIOLOGY 



(A) the germicidal power of strong solutions of the non-poisonous and nutri- 

 tive sugar, molasses, etc. 



It is entirely possible to measure the force of the osmotic process in some 

 of the above cases. Thus it may be accomplished for b by jackets of wood 

 held together by spiral springs or even by rubber bands, the roots being later 

 replaced by weights hung from one jacket. For g the seeds may be made 

 to break thick glass bottles, or may be made to record a part of their pres- 

 sure by an apparatus invented by MAcDouGAL, 176, though a simple dyna- 

 mometer devised for the purpose by RICHARDS (Torreya, i, 1901, 8) is 

 erroneous in principle (the same journal, 47, 70); a variety of other experi- 

 ments upon this subject is given by OSTERHOUT in his "Experiments with 

 Plants"; h may be very neatly tested by making up a-series of solutions of 

 sugar, e.g., molasses, shaking into each the same quantity of yeast, and noting 

 in which solution fermentation can just take place. 



There are some special phases of absorption to which the 

 student should give attention, especially the occasional, and 

 somewhat pathological, absorption of water by green leaves and 

 stems, and the important absorption by special structures in 

 epiphytes. Absorption by cut shoots will be considered later 

 under Transfer. 



So much for the general and physical aspects of osmotic 

 absorption. We turn now to consider the actual absorption 

 of water by the common land plants, and naturally the first 

 problem to present itself is this: 



In what quantity and under what pressures do roots osmotic- 

 ally absorb water? 



It is not experimentally practicable to test the individual absorb- 

 ing rootlets, but the collective action of these, as manifest by the quan- 

 tity passed from root to stem, may be determined. 



EXPERIMENT. Select a vigorous single-stemmed, firm-textured 

 plant, and cut away the stem near its transition to root, preferably 

 about 2 cm. above the surface of the ground ; over the stump slip a 

 tight piece of rubber tubing projecting a centimeter beyond; into the 

 projection insert a tight stopper containing a slender bent tube which 

 leads to a measuring-glass containing some oil (to prevent evapora- 

 tion). Water the plant properly (page 40) and observe, with calcu- 

 lation for that left in the tubes, the amount of water exuded by the 

 plant. 



EXPERIMENT. To the stump of a similar plant attach by a pres- 

 sure-tight joint a suitable pressure-gauge, and, properly watering the 

 plant, observe the pressure developed. 



MATERIALS. These are fully described, with quantities and with direc- 



