LATICIFEROUS CELLS 153 



Umbelliferae. In the St. John's Wort and certain other cases 

 the secretory cavities of the leaf are replaced by canals in the 

 stem, but it may be pointed out that the difference is one of 

 shape, not of kind. 



It is a familiar fact that in some plants a milky, though 

 sometimes coloured, juice (brilliant orange in the Greater Celan- 

 dine, Chelidonium majus) issues from every cut or broken surface. 

 This latex is especially found amongst British plants in members 

 of the Poppy-family (Papaveraceae) , Spurge-family (Euphorbiaceas) , 

 Harebell-family (Campanulaceae) , the tribe Liguliflorae of Com- 

 positae, and in the White Convolvulus (Convolvulus sepium) ; but 

 it is still more characteristic of certain tropical genera. The 

 latex is contained in much elongated tubes which constitute a 

 branched system throughout the thin-walled tissues of the plant 

 and which conform to one of two types. 



In the Spurges (e.g. Wood Spurge, Euphorbia amygdaloides) 

 the laticiferous tubes can be recognised already in the embryo 

 as several isolated cells, situated just outside the rudimentary 

 vascular system of the cotyledonary node. Each of these lati- 

 ciferous cells elongates considerably as the seedling develops, 

 insinuating itself between the surrounding parenchymatous cells, 

 and this process of growth continues throughout the life of the 

 plant. Thus, even in the adult condition, the number of lati- 

 ciferous cells remains the same as in the embryo. In the course 

 of their elongation the laticiferous cells develop frequent branches 

 which follow a more or less longitudinal course into all the organs 

 of the plant, including the different parts of the flower, but the 

 branches do not fuse with one another. In spite of this extensive 

 growth, which leads to the penetration of the latex-tubes even 

 into the ultimate branches in tropical Spurges as much as 

 50 feet above the ground no cross-walls arise in these elements. 

 On the other hand, as elongation and branching occur, repeated 

 nuclear division takes place, the numerous minute nuclei in the 

 adult laticiferous cell being embedded in the lining layer of 

 cytoplasm which envelops a continuous vacuole occupied by 

 the latex. 



In transverse sections through the mature stem of a Spurge, 

 the branches of the laticiferous cells (Fig. 77, 1.) will be seen at the 

 outer limit of the phloem (f>h.) as a number of large circular elements 



