142 



PART II.— VEGETABLE HISTOLOGY. 



invert sugar ; and still other ferments, as papain or papayotin, 

 obtained from the green fruit of the Paw-paw, and a ferment 

 similar to pepsin, found in the glandular hairs of the Sundew, 

 have the power to transform proteid matters into peptone. 



Neutral Principles. Under this head are included numer- 

 ous other neutral organic compounds, found in solution in the 

 cell-sap, that cannot properly be included under any of the 

 above heads. The term is not here used in any strict scientific 

 sense, but simply as one of convenience, to include a hetero- 

 geneous collection of compounds — some quite complex, others 

 relatively simple — whose chemical relations are not yet well 

 determined. Some authors also include under this head the 

 neutral glucosides and the non-alkaloidal amides. 



Fig. 384. 



Fig. 



Fig. 386. 



Fig. 384. — Calcium oxalate crystal from the petiole of Regonia. Magnified about 500 

 diameters. 



Fig. 385— Calcium oxalate crystal from the leaf of Agave Magnified about 300 

 diameters. 



Fig. 386, a, b. — Another form of crystals from Agave. Magnified about 200 diameters. 



Here are classed such principles as aloin (C 15 H 16 7 ), derived 

 from Socotrine aloes ; quassin (C 10 Hi 2 O 3 ), derived from the wood 

 and bark of Picraena excelsa and of Quassia amara ; santonin 

 (Ci 3 H 18 3 ), derived from Levant Worm-seed, and picrotoxin 

 (C9H01OJ, derived from the seeds of Animirta paniculata, a 

 plant belonging to the Moonseed family. Some of these princi- 

 ples are harmless, others are valuable medicines, and still others, 

 like picrotoxin, are active poisons. Although their origin and 

 uses to the plant are not thoroughly known, they are probably, 

 most of them, to be regarded as waste products of tissue meta- 

 morphosis. 



