192 A TEXT-BOOK OF BOTANY. 



III. Rosette aggregates or clustered crystals sometimes accom- 

 panying other forms are found in the following families : Acantha- 

 ce^e, Begoniaceae, Boraginacese, Calyceraceas, Campanulaceae, Can- 

 dolleaceae, Chenopodiacese, Chloranthacese, Elatinaceae, Empetra- 

 ceae, Gentianaceae, Gesneraceae, Hydrophyllacese, Labiatae, Loasa- 

 ceae, Magnoliaceae, IMelastomaceae, Alelianthaceae, Myristicaceae, 

 Nepenthaceae, Nymphaeaceae, Onagraceae, Papaveraceae, Phytolac- 

 caceae, Piperaceae, Polemoniaceae, Ranunculaceae, Sarraceniaceae, 

 and Turneraceae. 



IV. Sphaerites (sphere-crystals), or rosette aggregates com- 

 posed of very small needles, have been observed in certain plants of 

 the following families : Aceraceae, Asclepiadaceae, Berberidaceae, 

 Cactaceae, Combretaceae, Crassulaceae, Empetraceae, Euphorbiaceae, 

 Geraniaceae, IMelastomaceae, Papilionaceae, Phytolaccaceae, Rosa- 

 ceae, and Solanaceae. 



V". Raphides are sometimes associated with other forms of 

 crystals, as micro-crystals, rosette aggregates, rhombohedra, and 

 styloids. They are widely distributed among the ^Monocotyledons 

 and occur in the following Dicotyledons : Geraniaceae, Gesneraceae, 

 IMelianthaceae, Phytolaccaceae, Rubiaceae, Rutaceae, Saxifragaceae, 

 Theaceae, Urticaceae, and Zygophyllaceae. 



PLANT PROTEINS. 



The proteins are nitrogenous compounds, most of which con- 

 tain sulphur and some of which contain phosphorus. Their con- 

 stitution or the molecular structure of their molecules has not 

 been determined, but they are very large, and are built up of amino- 

 acids, the simplest of which is glycocoll (amino-acetic acid). 



Apart from the protoplasm found in living cells, the propor- 

 tion of proteins in plants is relatively small, except in seeds, where 

 they serve as nutriment during the germinating period, being made 

 available by the action of proteolytic enzymes. Most of the plant 

 proteins are globulins, and collectively have been termed phyto- 

 globulins. (i) The globulins are insoluble in pure water and in 

 dilute acids, but are soluble in dilute solutions of sodium chloride 

 ( I to 20 per cent.), afnmonium chloride, sodium sulphate and 

 dilute solution of potassium hydrate, from which solutions they 

 jnay be precipitated by dilution, dialysis, or acidification with CO2 



