CELL-CONTENTS AND FORMS OF CELLS. 239 



the nature of an emulsion, consisting of small globules, varying 

 from 0.0005 to 0.005 mm - m diameter. It is of variable com- 

 position and may contain certain hydrocarbons, as in pure 

 caoutchouc and pure gutta percha, oils, resins, mucilage, starch, 

 calcium oxalate, and alkaloids. 



Latex is found in three distinct types of tissues, differing 



FIG. 127. Study of Latex: A, tangential-longitudinal section through root of Taraxa- 

 cum, showing laticiferous vessel (m), sieve tube (s), parenchyma (p). B, the bark of 

 Euonymus, fractured and showing the thread-like latex (c) between the pieces (b). C, the 

 fragments of thread-like latex of Euonymus viewed under the microscope, and distinguished 

 from fibers by their dissolving in chloroform. A, after Meyer; C, from drawing by Hogstad. 



from each other in origin and manner of development. I. Laticif- 

 erous cells are long, tubular cells which arise in the initial cells 

 of the embryo and continue to elongate, keeping pace with the 

 growth of the plant, branching and traversing all of its organs'. 

 They may extend through the cells of the pith, bast, and primary 

 cortex, run along the veins of the leaf, being found occasionally 

 in the mesophyll, and extend into the fruit. Cells of this kind 



