LESSON 7.] BAPHIDES. 21 



nandra Gutta ; the chief difference between this gum and India-rubber 

 appears to be, that the milky juice that yields it (the latter) contains a 

 greater amount of starch. 



126. The milky juice, above referred to, is contained in a system 

 of distinct vessels (Fig. 26), called lactiferous (lacta, milk) ducts; 

 this structure may be easily seen in the India-rubber tree (Ficus 

 elastica). Dandelion, Lettuce, Celandine, and the various species of 

 Ficus and Euphorbia. 



127. Some of these milky juices are bland, as in the Cow-tree 

 (Oalactodendron utile] ; others are narcotic, as in the Poppy and 

 Lettuce ; others purgative, as Gamboge ; others diuretic, as Dandelion 

 (Taraxacum). 



LESSOR YII. 



EAPHIDES. 



128. In addition to the various forms of cell contents already 

 enumerated mineral matter, having either lime as its basis, or silica 

 (flint), is abundantly found. Where flinty matter obtains, it fre- 

 quently assumes an acicular or needle-like shape hence called 

 JRaphides, from the Greek raphis, a needle. 



129. The needle shape is not, by any means, universal ; they are 

 as frequently found of a Stellate (star) form, and not unfrequently as 

 single crystals, having an octohedral (eight sides), rectangular (right 

 angled), or prismatic (in form of a prism) form. 



130. No part of the plant appears to be free from them ; they are 

 found in the stem, bark, leaves, stipules, sepals, fruit, root, spiral-ves- 

 sels, and even in the pollen. 



131. Some plants are known to secrete Oxalic acid, which is a 

 fatal poison to man, and many other animals. 



132. To counteract the effect of this vicious material, and neu- 

 tralize it, such plants (Onion, Pie-plant or fihubarb), feed greedily 

 upon Carbonate of lime. This earth has great affinity for the 

 oxygen of Oxalic acid ; they seek each other, combine, and in the form 

 of crystals of varying figure, the new compound is deposited in cells 

 as the Oxalate of lime a perfectly innocuous combination. 



133. By this simple and beautiful arrangement, delicious and 

 nutritious vegetables are redeemed to the use of man, which, other- 

 wise, would prove speedily fatal to him. 



