LATEX OR MILK TUBES. 87 



CHAPTER XXI. 



LATEX OR MILK TUBES. 



Many plants, when wounded, emit a milky fluid varying in 

 color, copiousness, consistency and chemical composition in 

 different plants. This is called the latex, hence the name lati- 

 ciferous tissue. This tissue differs considerably in different 

 plants and is not confined to any particular region or tissue 

 system, but it is most common and abundant in ordinary par- 

 enchyma. 



The cells of milk tissue are of two kinds simple and com- 

 plex or branching. 



The simple latex tubes consist of long cells of indefinite 

 length running lenthwise of the plant with only a few branches. 

 Each tube with its few branches is believed to be a single cell. 

 In cross-section they are distinguished from parenchyma cells 

 by their smaller diameter and by being filled with opaque and 

 densely granular substances. The cell-walls are cellulose. The 

 complex tissue consists of greatly branching tubes, the 

 branches uniting cross-wise and forming a complex network in 

 the plant. 



Latex is of the nature of a waste or excretory product, 

 although it contains albumin and carbohydrates. It contains 

 resins and gums in solution and oily matters, often alkaloids 

 and organic acids. It coagulates and forms a sticky mass upon 

 exposure to the air. India rubber is an example of such dried 

 latex. Latex varies in color in different plants; it may be 

 white, yellow, orange, etc. In Bloodroot it is reddish. 



Stems of plants in which latex tissue is to be studied should 

 be cut into pieces and immediately put into strong alcohol, 

 which coagulates the latex and prevents it from running out of 

 the tubes. 



SIMPLE LATEX TUBES. 



These may be studied conveniently in Euphorbia and Milk- 

 weed plants. Make cross-sections of the stem of one of the 

 Milkweeds, stain in methyl-green and mount in water. The 

 milk tubes occur in the pith and bark and are distinguished 

 from the neighboring parenchyma cells by their smaller size 

 and densely granular, more deeply-stained contents. 



Examine a longitudinal section stained in methyl-green. 

 Lying among the parenchyma cells will be found long tubes 

 filled with dense, granular matter, wavy and with only an occa- 

 sional branch. The branches, when present, do not unite with 

 those of a neighboring tube. Each tube, however long, may be 

 looked upon as a single cell. 



