ELEMEXTARY STEUCTTJEE. 



45 



of an inch in diameter. They derive their name from containing 

 a watery fluid called latex, which when exposed to the air be- 



comes milky, 

 as in the 



and is either white. 



Dandelion, 



spurges, 



Figs. 89 and 90. Laticiferuus 



Poppy, India-Rubber, Lettuce, &c. ; 

 or coloured ; thus yellow latex is 

 well seen in the Celandine. The 

 latex has a number of granules or 

 globules floating in it, which are 

 composed of caoutchouc, or analo- 

 gous gum-resinous matters, and, oc- 

 casionally, mixed with them may 

 be observed peculiar-shaped starch 

 granules, as in Euphorbia {fig. 91). 

 Fremy states that in certain plants 

 he has found a kind of latex as 

 albuminous as the serum of the 

 blood or the albumen of the egg, 

 and to which he has given the name 

 of albuminous latex. Latieiferous 

 vessels were first discovered by Schultz, who also described the 

 latex as constantly circulating in them, and hence the term 

 Cinenchyma or moving tissue has been applied to them. Lesti- 

 boudois has also, within the last few 

 years, made out a circulation of the con- 

 tents of latieiferous vessels. Trecul has 

 endeavoured to prove that the latieiferous 

 vessels are in direct connexion with 

 the spiral and other vessels, and he 

 concludes that they act as venous reser- 

 voirs to the circulating fluid. Those 

 vessels occur especially in the inner 

 bark of Dicotyledons, in the pith, and 

 in the stalks and veins of leaves. They 



are also to be found in the vascular bundles of Monocotyledons 

 and all parts which are prolonged from them. In Acotyledons 

 they exist only in the higher orders. 



Their nature or origin is not we'l ascertained. By some vege- 

 table anatomists they are considered to be formed, like the 

 ordinary pitted vessels, from rows of cells arranged in various 

 directions with respect to each other, the partitions between their 

 cavities being more or less absorbed, so that they communicate 

 freely together. There can be little doubt, however, that they 

 are simply Intercellular passages, which form a network of canals 

 (see Intercellular System), and which have originally no proper 

 membrane, but appear to acquire one subsequently by the depo- 

 sition of matter of varying thickness from the secretions which 

 they contain. 



J 



F/fiT. 91.Latioi- 

 feious vessels 

 from a species 

 of Euphorbia ; 

 the larex con- 

 taiiiiiiffstarch 

 graiiu'e* of 

 a peculiar 

 form. From 

 Henfrey. 



