DEFENSIVE EQUIPMENT OF PLANTS = 143 
stitute reserves of food—e.g., walnuts, brazils, castor-oil 
seeds, linseed, etc. 
(e) Volatile Oils——These give to plants their scent. In 
flowers they act as an attraction to the pollinating insects, 
but in many cases the whole plant is strongly scented— 
e.g., mint, lavender, sage. Camphor is an aromatic 
crystalline substance distilled from the wood of the 
camphor-tree ; it is poisonous. 
(f) Caleium Oxalate.—This salt is poisonous, but it is 
produced naturally in the economy of plants, as a by- 
product in the assimilation of proteins. It is generally 
deposited in the form of hard gritty crystais within the 
tissues (rhubarb-roots). In combination with potash, 
oxalic acid occurs in sorrel. Crystals of calcium oxalate 
are specially abundant in the outer leaves of some bulbs, 
where they certainly serve a protective purpose. On one 
occasion at Kew the outer leaves were stripped off the 
bulbs of the Roman hyacinth; but the bulbs, thus 
deprived of their protective armour, were found to be 
quickly destroyed by snails. 
(g) Free Acids.—These occur very commonly in unripe 
fruits. making them sour and uneatable. Citric acid is 
abundant in the lemon, but in smaller quantities it is 
present in many of our commonest fruits—e.g., cranberry, 
cherry, and rose-hips. Mixed with an equal proportion of 
malic acid, it is found in raspberries, red and black cur- 
rants, bilberries, and wild strawberries. Unripe apples 
and pears contain malic acid only. As the starch of the 
unripe fruits becomes converted into sugar, these acids 
gradually disappear, and the fruits become sweet and 
palatable. 
(h) Alkaloid Poisons.—The most deadly organic poisons 
known to the chemist are found in plants. Digitalin is 
obtained from the leaves of the foxglove (Digitalis pur- 
purea) ; strychnin from the seeds of Strychnos Nua-vomica ; 
belladonnin and atropin, from the deadly nightshade 
(Atropa Belladonna); aconitin from the root of Aconi- 
tum Napellus ; morphia from the opium-juice crushed 
out of the unripe capsules of the poppy (Papaver somni- 
ferum). But in most of these cases the whole plant is more 
or less poisonous, and this may extend even to the flowers 
and fruits. In the aconite the very honey secreted in the 
flower is poisonous. 
