COMMON OBJECTS WORTH EXAMINING. 289 



to close the little apertures between the fibres of the 

 gold lace. By breathing through these little openings 

 the moisture will at any time start the spores on their 

 "quadrupedal hornpipe," and when they are dry the 

 performance may be repeated. An ordinary cell with 

 the cement ring cut into narrow parts by the strokes of 

 a penknife, so that the moisture could enter, would prob- 

 ably 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 of many plants. They occur in 

 four different and easily recognizable forms as follows : 



a. Raphides. Small needle-like crystals, with long 

 shafts very gradually tapering to the pointed ends. 

 They are usually found collected together in loose bun- 

 dles, and generally within a distinct cell. They are 

 abundant in Lemna, in common Spiderwort (Trades- 

 cdntia), Touch-me-not (Impdtiens falva), the Primrose 

 (Onothera\ the Golden -club (Orontium aqudticum), 

 Virginia creeper (Ampdopsis quinquefolia), and many 

 others. 



1}. Sphcerdpkides. More or less spherical forms, 

 smooth, or with the entire surface roughened by crystal- 

 line projections. They usually occur within a distinct 

 cell, and are to be found in the Oleander (Nerium), Ge- 

 ranium, Oxalic, Bouncing Bet (Sapondria officindlis), 

 Fleabane (Erigerori), Portulaca, Hibiscus, common mal- 

 low (Mdlva rotundifolia\ and others. Yery remarka- 

 ble crystals are found in the epidermal cells of the stem 



