CELLULAR TISSUE. 233 



Variously-cut sections of leaves should be made, and slices 

 taken parallel to the surfaces at different distances, for the 

 purpose of microscopic examination. 



Among the cell-cortents of some plants, are beautiful 

 crystals called Raphides : the term is derived from pa<ig, 

 a needle, from the resemblance of the crystal to a needle. 

 They are composed of the phosphate and oxalate of lime ; 

 there is a difference of opinion as to their use in the 

 economy of the plant. "Whether the result of chemical 

 affinity, or of a vital process, cannot be decided ; but it is 

 certain that they can be produced artificially in the tissue 

 of plants." 



The French philosopher, Geoffrey St. Hilaire, endeavoured 

 to prove that crystals are the possible transition of the 

 inorganic to organic matter. Crystals have naturally been 

 supposed to conceal the first beginnings of the phase 

 named organic, because in crystals we first meet with 

 determinate form as a constituent element. The matter 

 named inorganic has no determinate form ; but a crystal 

 is matter arranged in a particular and essential form. The 

 differences, however, between the highest form of crystal 

 and the lowest form of organic life known a simple re- 

 productive cell are so manifold and striking, that the 

 attempt to make crystals the bridge over which inorganic 

 matter passes into the organic, is almost universally 

 regarded as futile. 1 



If we examine a portion of the layers of an onion, fig. 

 140, No. 1, or a thin section of the stem or root of the 

 garden rhubarb, fig. 140, No. 4, we shall find many cells 

 in which, either bundles of needle-shaped crystals, or 

 masses of a stellate form occur. 



Raphides were first noticed by Malpighi in Opuntia, 

 and subsequently described by Jurine and Raspail. 

 According to the latter observer, the needle-shape or 

 acicular are composed of phosphate, and the stellate of 

 oxalate of lime. There are others having lime as a basis, 

 in combination with tartaric, malic, or citric acid. These 

 are easily destroyed by acetic acid, and are also very soluble 

 in many of the fluids employed in the conservation of ob- 

 jects; some of them are as large as the l-40th of an inch, 

 others are as small as the 1-1 000th. They occur in all 



(1) See Addenda. 



