168 PLANT PHYSIOLOGY 



of occurrence of the color. Also, in the experiment with white flowers 

 observe the exact location of the red color. 



Ascent in Lumina or Walls. Fill the lumina without injury to the walls 

 in a shoot as follows. In a water-bath in a shallow dish (such as a paint 

 mixer 5 cm. in diameter) warm cocoa-butter colored by lampblack until 

 it just melts (which will occur at 33°, a temperature harmless to the plant), 

 and warm pure water in a similar dish (for a control). Select a convenient 

 herbaceous plant, which has been allowed to become somewhat dry (to 

 develop negative pressure explained below), bend its stem at one point 

 beneath the melted cocoa-butter and sever it there, cutting another similar 

 shoot under the water. At once transfer both to a dish of fresh water, and, 

 as soon as the butter is hardened, scrape a thin layer from the cut end in 

 order to get rid of surplus butter and to expose the walls as well as the filled 

 lumina to the water. Note the comparative rate of wilting of the two shoots. 

 Or this can be done also with gelatin as described by Detmer, 227. 



Motility in Wood. Cut a fresh cylinder some 5 cm. long and 1 cm. diam- 

 eter from growing pine or other coniferous wood, and soak it in pure water. 

 Then, shaking it clear of all water, place a drop on the top and note any 

 result at the bottom; also invert the piece and repeat the test. Over one 

 end of a similar piece 1 cm. long fit a stout rubber tube through which clean 

 water is to be forced under a known pressure, obtained either by a water 

 column, or preferably by mercury pressure in a U tube; observe the amount 

 which filters through the wood in a given time. Then in precisely the same 

 way test a cylinder cut in the tangential, and one cut in the radial, direction. 



Continuity of Vessels. Stir some fine cinnabar in distilled water, and 

 filter repeatedly until a mixture is left in which the cinnabar will not settle 

 for days. Then, using the apparatus of the preceding experiment, force 

 the mixture under pressure into longitudinal cylinders of different kinds of 

 wood, and note whether the passing water contains the cinnabar. Later 

 make longitudinal sections of the wood, and note under the microscope the 

 distribution of the cinnabar. 



Negative Pressure in the Vessels. Select two similar herbaceous plants, 

 and keep one dry (unwatered in a dry room) and the other very moist (by 

 ample watering in a damp chamber or bell jar in darkness). Cut a shoot 

 of each (a) under a strong solution of eosin, (6) under mercury, (c) under 

 melted colored cocoa-butter, and at once make longitudinal sections and 

 examine microscopically with reference to penetration of the substances 

 into the ducts. If a translucent stem is used, the height to which the 

 liquid jumps can be viewed directly by holding up to the. light. Also select, 

 a half dozen different herbaceous plants, allow them to become partially 

 dry; then cut from each two shoots, one under water and one in air- place 

 Both in water and observe the comparative rate of wilting. The cutting in 

 all these cases is best effected by use of small pruning shears. 



This negative pressure in the conducting system of plants, 

 due to rarefaction of the air-bubbles in the vessels under in- 

 fluence of very rapid removal of water from the stem by trans- 



