TRANSPORT 167 



7. TRANSPORT. 



Having considered the absorption of substances into the 

 plant, we must next study the mode of movement, or transport, 

 of those substances from place to place. In practice it is con- 

 venient to separate the subject into two parts, the movement 

 of pure water through the plant, a process sometimes called 

 transfer, and the movement of elaborated food substances from 

 place to place, commonly called trans location. 



(a) Transfer. 



Turning first to transfer, it is plain that a certain amount 

 thereof is provided by osmotic movement from cell to cell, but 

 this is wholly inadequate to explain the rapidity with which great 

 quantities of water are moved throughout the plant to make 

 up the loss from transpiration, a process soon to be studied. 

 Unfortunately our knowledge of this subject, despite much study t 

 is still very imperfect, and the experimental study is mostly in a 

 corresponding condition. The student can doubtless spend his 

 experimenting time to better advantage upon other subjects, 

 working this out through the literature, but if he can follow it 

 practically he will be aided by the following : 



SUGGESTED EXPERIMENTS. Rate of Ascent. Cut under water a trans- 

 lucent colorless shoot, such as Impatiens; transfer it to a strong solution 

 of eosin or methyl green (or red ink), and observe the rise of the color in 

 the fibrovascular bundles to the leaf. Or use shoots having pure-white 

 flowers, and note the time needed for these to show the color. Or, and 

 better, follow SACHS' method of watering the plant with lithium nitrate, 

 which can readily be recognized by the spectroscope in samples of tissue 

 taken at different heights. (Note fuller directions in DETMER, 233; and there 

 is very valuable matter in a paper on "Color in Plants" by KRAEMER in 

 Bulletin of the Torrey Botanical Club, 33, 1906, 77.) 



Path of Ascent. Select a shrubby plant, such as a rose-bush; remove 

 the bark on one branch in a ring all around, i cm. long, and, to prevent 

 drying out, cover the place with vaseline or grafting-wax. Also, remove a 

 similar ring on another branch, but including also the wood for 2 mm. deep, 

 and cover as before. Note the effect upon water transfer as shown by 

 the wilting of the leaves. 



After the shoot placed in eosin, as described above, shows signs of red 

 in the leaf-veins, cut cross-sections at various heights and observe the place 



