STEMS 



721 



and Sapotaceae, the latter family including Palaquium, which furnishes 

 the gutta percha of commerce. The second and commonest kind of 

 latex tissue is that in which the cells fuse (as in tracheae) by the resorp- 

 tion of the connecting walls, thus forming syncytes known as laticiferous 

 vessels, which form a connected cortical system throughout the plant 

 (fig. 1038). Sometimes the cells fuse in rows, as in the celandine poppy, 

 thus forming an easy transition 

 to rows of latex sacs. More 

 commonly there is lateral as 

 well as terminal fusion, result- 

 ing in an anastomosing net- 

 work, as in the milky- juiced 

 composites (Cichorieae) ; simi- 

 lar laticiferous vessels charac- 

 terize the fungus Lactarius. 

 The third and most extraor- 

 dinary kind of laticiferous tissue 

 is that cha.ra.cterizlngEuphorbia 

 and the milkweeds (Asclepia- 

 daceae), where the laticiferous 

 element is a coenocyte, arising 

 in the embryo from a single 

 ordinary cell. Later this de- 

 velops at an equal rate with 

 the plant, penetrating among 

 the cells as do the hyphae of 

 a parasitic fungus, and sometimes attaining a length of several meters; 

 branching occurs freely, but the branches rarely anastomose. In all 

 cases latex tissues occupy definite regions and traverse the entire plant, 

 as do vascular tissues. 



The contents of latex tubes. Latex elements, whether they are cells, 

 syncytes, or coenocytes, contain an extraordinary assemblage of sub- 

 stances. Latex consists of a watery fluid, which holds in suspension 

 gums, resins, caoutchouc, fats, and waxes, and therefore is an emulsion; 

 in addition there are held in solution tannins, soluble gums, sugars, 

 alkaloids, salts, and occasionally proteolytic ferments (as papain in 

 Carica Papaya). Leucoplasts, elaioplasts, and proteinoplasts occur in 

 the latex, organizing respectively starch grains, oil bodies, and protein 

 granules; in Euphorbia there are starch grains of unusual shape, re- 



FiG. 1038. A longitudinal section through 

 a portion of a root of the prickly lettuce 

 (Lactuca scariola), showing the anastomosing 

 latex tubes (<); note the absence of cross 

 walls; highly magnified. 



