PROTEINS OR ALBUMINOIDS 



i6s 



Fig. 80), (2) radiating crystal aggregates {b), or (3) bundles of 

 needle-shaped crystals or raphides (c). The latter form is 

 frequent in the cells of many monocotyledons. 



Malic, citric and tartaric acids are also found free or combined 

 with lime or potash, especially in unripe fruits of various kinds. 

 A. lemon contains from 5 to 7 per cent, of free citric acid. 



Ex. 92. — Mount a very small portion of rhubarb jam in water, and look 

 for crystal-aggregates of calcium oxalate resembling i, Fig. 80. Many will 

 be observed within the thin parenchymatous cells present in the jam. 



Ex. 93. — Treat some clover, vetch, fuchsia and other leaves with Eau de 

 Javelle as in Ex 75, wash in water and mount a small piece in glycerine : 

 note the form of the crystals of calcium oxalate, and their position in the 

 leaves. In which special tissues of the leaves are they most abundant ? 



II. Nitrogenous Organic Substances. 

 These compounds contain nitrogen and frequently other 



Fig. St.— I. Transverse section of a wheat-grain. ^ Pericarp ; a ' aleuron-layer ' ; 6 starchy 

 part of the endosperm ; yf urrow at back of the grain. 



3 Part A of I (enlarged i6o diameters). > Pericarp ; a ' aleuron-layer ' showing small 

 aleuron-grains anda central nucleus within each cell ; 6 cells of endosperm containing starch- 

 grains. 



elements such as sulphur and phosphorus, in addition to carbon, 

 hydrogen and oxygen. 



The most important examples are the proteins or albuminoids 

 amides and alkaloids. 



I. Proteins or albuminoids. — The proteins are exceedingly 



