78 VEGETABLE HISTOLOGY. 



ally massed in a compact bundle, like a wheat-sheaf, occupying 

 a large part of the interior of the cell. Raphides are by no 

 means of such general occurrence as ordinary crystals, being 

 restricted to certain orders. 



Soak a slice of the scale of a squill bulb in water just long 

 enough to soften it and then place in a mixture of alcohol and 

 glycerin 6-8 hours. Make thin sections and mount in glycerin. 

 The tissue is composed of large, clear, typical, parenchyma cells, 

 with here and there a cell filled with long needle crystals, 

 together with mucilage. 



Apply a drop of acetic acid. The needles do not dissolve. 

 To another section add hydrochloric acid; the needles dissolve 

 without effervescence, showing that they are calcium oxalate. 

 Had they been carbonate they would have dissolved in acetic 

 acid with effervescence. 



SECRETION RESERVOIRS. 



These differ from intercellular air space only in being filled 

 with secretions instead of air. They differ from secretion sacs 

 in that they are spaces surrounded by a number of cells, while 

 the sacs are single cells. The reservoirs are often merely irreg- 

 ular spaces left by the breaking down of one or more cells, but 

 they sometimes have a remarkable regularity of form and clear- 

 ness of outline. 



It has been observed that these spaces are not, as a rule, met 

 with in plants having the simple secretion sacs. The cells 

 which surround the more complete cavities are quite different 

 from the other parenchyma cells, and they are collectively 

 called the epithelium of the spaces. These are the secreting 

 cells and the secreted matters are discharged in some manner 

 into the reservoirs, where they accumulate. 



Cut cross-sections of a pine needle between pith and mount 

 in water or chloral hydrate solution. Arranged around the 

 section near the periphery are five or six cavities, each having 

 a lining epithelium of flattened, thin-walled cells, and next to 

 these is a circle of glistening, very thick-walled cells (Fig. 62). 

 These structures are channels which carry the turpentine 

 secretion. Also make cross-sections of the stem of a softened 

 clove bud and mount in water. Near the circumference will 

 be found a double row of large cavities, each lined with a mem- 

 brance of secreting cells. The cavities carry the "oil of cloves." 



