54 



BOTANY OF THE LIVING PLANT 



many distinct nucleated cells, by the absorption of their septa : while the 

 contents which have previously assumed the character of the secretion flow 

 together, though their nuclei may still persist (Fig. 32, B). New branches 

 may also be formed which anastomose freely, so that a dense network of tubes 

 results. This type of latex-vessel is found in the Chicoriaceae, Campanulaceae 

 and Papaveraceae, and they are found also in Manihot and Hevea (the chief 

 rubber-yielding tree), among the Euphorbiaceae. The other type, occurring 

 in most of the Euphorbiaceae, the Urticaceae and Apocynaceae, consists of 

 much-branched cells which do not juse. They may be recognised in the young 



A 



Fig. 32. 



A. — Diagrammatic section of the hypocotyl of Tragopogon, showing the position 

 of the latex-vessels relatively to the other tissues. 



Z?.— Latex-vessels from a longitudinal section of a cotyledon of Tragopogon, 

 showing the absorption of the cell-walls in progress. (After Scott.) 



embryo : they grow with the growth of the various tissues, branching fre- 

 quently, and thrusting their ends between the cells of other tissues. They 

 contain the milky latex and numerous nuclei, which divide actively near to 

 the growing tips of the tubes. 



The function of the latex-tubes is uncertain. They have been regarded 

 as storage elements or as a channel for transport of organic materials through 

 the plant. Their contents include proteins and carbohydrates, caoutchouc 

 and resin. It is uncertain to what extent these materials can be again used 

 by the plant. The structure of the latex-tubes, and their close relation to 

 the mesophyll of the leaf and to the phloem of the vascular strands (Fig. 32, A), 

 lend some support to the suggestion that the tubes are connected with 

 transport. 



Calcium oxalate is found as solitary crystals laid aside in cells scattered 

 through the tissues of many plants (Figs. 34, 47). But it may also take the 

 form of numerous long acicular crystals, or raphides, which lie parallel to one 



