3o6 AQUATIC MICROSCOPY FOR BEGINNERS. 



cell with the cement ring cut into narrow segments by 

 the strokes of a penknife, so that the moisture could 

 enter, would probably answer the purpose as well as 

 my friend's more elaborate contrivance. 



20. Plant, Crystals, already referred to (No. 15), 

 are found in the tissues jf many plants. They occur 

 in four different and easily recognizable forms as fol- 

 lows: 



a. Rdphides. — Small needle-like crystals, with long 

 shafts gradually tapering to the pointed ends. They 

 are usually found collected together in loose bundles, 

 and generally within a distinct cell. They are abund- 

 ant in Lemna, in common Spiderwort {Tradescdntia) , 

 Touch-me-not {Impdtiens ftilva), the Primrose (CEno^ 

 the'ra), the Golden-club (Ordntium aqudticum), Virginia 

 creeper {Ampelopsis quinquefdlia), and many others. 



b. SphcRrdphides — More or less spherical forms, 

 smooth, or with the entire surface roughened by crystal- 

 line projections. They usually occur within a dis- 

 tinct cell, and are to be found in the Oleander (Ne- 

 riuin), Geranium, Oxalis, Bouncing Bet {Sapondria of- 

 ficindlis) , Fleabane ' (Ertgeron) , Portulaca, Hibiscus, 

 common mallow {Mdlva rotilndifolid), and others. Very 

 remarkable crystals are found in the epidermalcells of 

 the stem of the common Richweed (jPilea pdmila), a 

 semitransparent plant growing in 'moist, shady places. 



c. Long Crystal Prisms. — These are long crystals, 

 with angular, prismatic shafts and angular tips. They 

 never occur loosely as do Raphides, but one or two 

 together in the tissue of the plant. They are abun- 

 dant in the cultivated Gladiolus, Flower-de-luce {Iris 

 versicolor), some of the Asters, in Cynthia Virginica, 

 Hawkweed {Hierdciutri), the Thistles (Cirsium), and in 

 others. 



