76 



Elementary Plant Physiology. 



solution of eosin. Note the appearance of the dye in certain 

 tissues a few hours later. What is the path of the ascending sap? 

 It is to be borne in mind that the color is diffused laterally from 

 the channels through which it is conducted in greatest volume. 

 To follow the course of the sap through a leaf, cut off a leaf, 

 and place the base of the petiole in an eosin solution for a few 

 hours. Remove, and hold up to light. 



It will be interesting also to place the base of the peduncle 



of some flower with white 

 petals in the solution, and 

 observe the course of the 

 sap in parts of the flower. 

 Ordinary red ink will serve 

 as a coloring fluid in all 

 of the above tests. 



71. Passage of sap 

 through a woody 

 stem. — Cut off a large 

 branch of oak, or cherry, 

 or any convenient tree, 

 and place the base of the 

 stem in a dish of water 

 for a short time, then in 

 a vessel containing col- 

 ored fluid, in which it 

 should be allowed to remain for a day. Remove, and wash off 

 adhering coloring matter, and cut away one side of the branch 

 nearly to the center as far upward as the color may be seen. 

 Through what part of the stem has the colored fluid ascended? 

 The capacity of the wood for the conduction of water depends 

 upon its age, and very marked differences are found between 

 the recently formed and the older wood. 



72. Rate of movement of water through stems. — 

 Cut off a stem of bean, sunflower, Bryonia, or Cucurbita under 



Fig. 53. — Transverse section of part of stem 

 of Sanihucus. e, epidermis ; ^, piiellogen ; 

 r/, cortex ; c, cambium ; /i, wood, tlirougii 

 which ascent of sap takes place ; m^, pith. 



