68 



HUTCHINSON'S POPULAR BOTANY 



(fig. 78). The non-nitrogenous compounds, which invariably contain the 

 elements carbon, hydrogen, and oxygen, are starch, sugars, inulin, and 



fatty oils. 



A word as to the fixed or fatty oils. One of the most valuable of these is 

 olive oil, which is obtained from the Olive (Olea europea), a shrubby tree 

 cultivated with great care in Spain, Italy, Syria, and other countries on the 

 shores of the Mediterranean Sea. The oil is contained in the drupe (fig. 79). 

 The Olive harvest in Italy and Spain produces 9,000,000 or 10,000,000 a 

 year. Palm-oil is obtained from the fruit of various Palms, and approaches 

 to the condition of ordinary fat ; so that it is well adapted for the manufacture 

 of candles. It constitutes an important article of food in those countries 

 where Palms abound. The Flax-plant (Linum) yields the valuable linseed- 

 oil, which is expressed from the seeds and largely used after distillation in 

 the preparation of paint. The pressed seeds from which the oil has been 

 partly extracted constitute the oil-cake often 

 given to cattle on account of its fattening pro- 

 perties. Rape-oil is extracted from the seeds of 

 the Rape-plant (Brassica napus}, and is the oil 

 best adapted for the lubricating of machinery; 

 while the seeds of a species of Poppy (Papaver 

 somniferum) supply the oil of that name ; and 

 those of the monkey-nut (Arachis hypogea] yield 

 the well-known ground-nut-oil, which is largely 

 used in India, Java, and Malacca both for light- 

 ing purposes and for food. The fatty oils may 

 be coloured black with osmic acid, or pink by 

 alkanna, and are soluble in ether. 



Crystalloids, to which reference was made a 

 paragraph or so back, must not be confounded 

 with true crystals. They resemble them in ap- 

 pearance, but are essentially different, being capable of swelling up when 

 treated with certain reagents, which true crystals are not. They are to be 

 met with in most oily seeds, as the seeds of the Castor-oil-plant (Ricinus 

 commums), and are not uncommon in the tuber of the potato. In the 

 latter they take a cubical form, and on being immersed in water split up 

 like a pack of cards, without dissolving (fig. 78). 



True crystals (fig. 80) are far more plentiful in vegetable tissues than 

 crystalloids ; for which reason they call for more extended notice. Plants 

 of the Cactus tribe (Cqctacece) usually contain a great quantity of oxalic 

 acid, which would be deadly to the plants were it not that they take up 

 from the soil a proportionate quantity of lime ; and this combines with the 

 acids in insoluble crystals. The Old-man Cactus (Cactus senilis) is computed 

 to contain as much as 85 per cent, of oxalate of lime ; and it often happens 

 with certain species of this tribe that their tissues become so loaded with 



FIG. 87. SCOTS PINE (Pinus 

 sylvestris). 



A. section of tissue showing the resin 

 passage (in the centre). 



