PART OF MOVEMENT OF LIQUIDS IN PLANTS. 6? 



through which a colored solution has been lifted by transpiration, we can 

 see small groups of the minute cells in the cambial ring which are col- 

 ored. These groups of cells which form strands running through the stem are 

 procambium strands. The cells divide and increase just like the cambium 

 cells, and the older ones thrown off on either side change, those toward the 

 centre of the stem to wood vessels and fibres, and those on the outer side to 

 bast cells and sieve tubes. 



123. Fibrovascular bundles in the Indian corn. In fig. 54 is repre- 

 sented a fibrovascular bundle of the stem of the Indian corn. The large 

 cells are those of the spiral and reticulated 



and annular vessels. This is the woody 

 portion of the bundle, or xylem. Oppo- 

 site this is the bast portion or phloem, 

 marked by the lighter colored tissue at i. 

 The larger of these cells are the sieve 

 tubes, and intermingled with them are 

 smaller cells with thin walls. Surround- 

 ing the entire bundle are small cells with 

 thick walls. These are elongated and the 

 tapering ends overlap. They are thus 

 slender and long and form fibres. In 

 such a bundle all of the cambium has 

 passed over into permanent tissue and the 

 bundle is said to be closed. 



124. Rise of water in the vessels. 

 During the movement of the water or 

 nutrient solutions upward in the stem the 

 vessels of the wood portion of the bundle 



Fig. 54- 



Transaction of fibrovascular bundle of 

 Indian corn. , toward periphery of 

 stem ; g-, large pitted vessels ; s, spiral 

 vessel ; r, annular vessel ; /, air cavity 

 formed by breaking apart of the cells ; 

 /". soft bast, a form of sieve tissue ; /, 



in certain plants are nearly or quite filled, thin- walled parenchyma. (Sachs.) 

 if root pressure is active and transpiration is not very rapid. If, however, on 

 dry days transpiration is in excess of root pressure, as often happens, the 

 vessels are not filled with the water, but are partly filled with certain gases 

 because the air or other gases in the plant become rarefied as a result of the 

 excessive loss of water. There are then successive rows of air or gas bub- 

 bles in the vessels separated by films of water which also line the walls of 

 the vessels. The condition of the vessel is much like that of a glass tube 

 through which one might pass the " froth" which is formed on the surface 

 of soapy water. This forms a chain of bubbles in the vessels. This chain 

 has been called Jamin's chain because of the discoverer. 



125. Rise of water in the bundles is not we' 1 understood. Why water or 

 food solutions can be raised by the plant to the height attained by some trees 

 has never been satisfactorily explained. There are several theories pro- 



