SCIENCE-GOSSIP. 



13- 



CHAPTERS FOR YOUNG NATURALISTS. 



(Continued from Vol. iv. p. 168.) 



CRYSTALS IN PLANTS. 

 By B. H. How. 



T T is a very interesting as well as extraordinary 

 fact that crystals composed of mineral sub- 

 stances are constantly to be found embedded in 

 the cells and cell-walls of plants. Sometimes 

 they are found as solitary crystals, and sometimes 

 in thickly-clustered groups. 



These crystals are true minerals, and are found 

 in two forms ; the first being composed of cal- 

 cium carbonate, and the second (which includes 

 by far the larger number) of calcium oxalate. The 

 latter is formed by sulphate of calcium being first 

 absorbed by the roots from the soil, and then when 

 it encounters oxalic acid in the plant it is decom- 

 posed by the acid combining with the lime, and 

 oxalate of calcium is the result. These crystals 

 generally crystallize into one of two systems, 

 depending on the proportion of water. The first 

 is the quadratic, and includes all the octahedral 

 forms. The second series is the clinorhombic, and 

 includes the acicular crystals called "raphides," 

 so named from the Greek word "raphides" or 

 needle. Masses of crystals are to be found in 

 walnut leaves, but particularly in monocotyledonous 

 plants, and in the bast tissue of trees. To see 

 crystals well a fairly powerful microscope is 

 necessary, but with the aid of an ordinary good 

 one their varied and beautiful forms may be easily 

 studied. 



In the cells of some plants, notably those of the 

 old-man cactus, crystals are so thickly embedded 

 that when the plant is dried, fully eighty per cent, of 

 the dried tissue is found to be composed of them. 

 In the locust-bark they are also very numerous, 

 but so small that a million and a-half has been 

 found in a square inch not thicker than writing 

 paper. Crystals are found very plentifully in the 

 stems of rhubarb. If a small portion of the pulp 

 be well boiled, then separated with a needle, after 

 a drop of water has been added to it, and placed 

 under the microscope, the needle-shaped crystals 

 will be easily seen. Small prismatic crystals lie 

 hid in the cuticle, or brown outer coat, of the 

 common onion. Many are also to be found 

 in lichens, on the outer surface of the walls of 

 the cells. 



Although crystals are formed first in the proto- 

 plasm of plants, they gradually find their way to 

 the cell sap and then to the inner or outer surface 

 of the cell-walls. If a little milky juice from the 

 dandelion be placed under a microscope it will be 

 seen to contain many beautiful raphides, and the 

 juice of the common hyacinth also contains them. 



They are found in the leaves of the bulb of the 

 medicinal squill, and in the stems of the Calla, the 

 Arum and the Aloe. In the Iris and the Turkey 

 rhubarb they are found in the roots. In the latter 

 they are so numerous as to give quite a gritty taste 

 if chewed. 



Sometimes plant crystals are so united as to 

 form beautiful stellate bodies, and occasionally they 

 assume circular crystalline masses, especially in the 

 Cactus family. Raphides are only found as a rule 

 in cells that contain no other granular contents. 

 Crystals in the form of cubicles are to be found 

 in some plants. Occasionally other substances 

 besides oxalate of lime are found crystallized, as 

 when on the under surfaces of the leaves of the 

 Deutzia scabia, a garden shrub, beautiful crystals of 

 silica can be seen in a stellate form. Crystals of 

 sulphate of lime are often found hidden in plants 

 of cycadaceous origin. Those composed of calcium 

 carbonate are found in the cell-walls of certain of 

 the Urticaceae and in the protoplasm of the Myxo- 

 mycetes — those extraordinary fungi which differ 

 so much from all the other fungi in structure, 

 being composed only of masses of protoplasm, 

 called "plasmodia." In the monocotyledonous 

 plants crystals can be easily detected, and in the 

 wood of conifers. 



The student must be careful not to confuse 

 crystals with crystalloids, which differ entirely in 

 their composition ; crystals being formed of mineral 

 and crystalloids of vegetable substances. The 

 latter are composed of " proteinaceous or nitro- 

 genous material, closely allied to protoplasm." In 

 shape and appearance they very nearly resemble 

 crystals, as they take cubical, octahedral, rhom- 

 boidal and tetrahedral forms, and in water are 

 insoluble. They are found in the tubers of potatoes, 

 in marine red algae, and in oily seeds, like those of 

 the Brazil nut. When they break up they appear 

 as if composed of several hard layers. One great 

 difference to be observed between them and crystals 

 is that they expand largely under the influence 

 of certain " re-agents," whilst true mineral crystals 

 do not. 



The study of crystals is indeed a most interesting 

 one, and will well repay the earnest student of 

 nature. Patient attention must be given to prepar- 

 ing subjects for the microscope, but when that is 

 done he will be amply rewarded by the beautiful 

 and varied forms that will meet the eye and delight 

 the heart. 



Bournemouth, 1898. 



