128 



THE AMERICAN BOTANIST 



latexes, and in one species the milk is actually dark blue. It is 

 interesting to note in this connection that nO' plant has a green 

 latex, common as this color is in other parts of the plant. 



Latex-bearing plants are not scattered promiscuously 

 throughout the plant world. Many plant families have no 

 laticiferous members but when latex occurs at all, it is quite 

 likely to be found in all members of such a group. Nor are 

 laticiferous plants very abundant. Among the fungi the phe- 

 nomenon is confined to the genus Lactarhis and a few of the 

 shelf fungi, such as the sulphur polypore, and in flowering plants 

 less than a dozen families of plants possess it. The best known 

 are the spurges (Euphorbiaceae), the dog banes (Apocynaceae), 

 the dandelion or chickory family (Cichoriaceae), the poppies 

 (Papaveraceae) the bellworts (Campanulaceae), the sumachs 

 ( Anacardiaceae) , the banana family (Musaceae) the Bread- 

 fruit family ( Artocarpaceae), and the milkweed family par 

 excellence (Asclepiadaceae). Most of these adhere pretty 

 closely to the production of a white juice, the mushrooms and 

 poppy-worts being the principal ones to exhibit different colors. 



It is a singular fact that all the composite flowers con- 

 structed on the plan of the dandelion, that is with heads consist- 

 ing entirely of ligulate flowers, have latex, while those with 

 ray and disk flowers like the sunflowers, and those with tubular 

 flowers like the thistles are without it. A few years ago, all 

 the composite flowers were placed in one great group, but they 

 are now regarded as constituting several closely related families. 

 Those who believe that the dandelion-like flowers should be 

 placed in a separate group may well adduce the possession of 

 latex as an additional reason for the separation. 



In laticiferous plants, the latex may occur in any organ of 

 the plant from the roots to the flowers and it may be present 

 in one part and not in another. Latex is not, as some suppose, 

 identical with the sap of plants. Latex tubes have no connec- 

 tion with the fibrovascular bundles through which the food and 



