I06 PLANT LIFE. 



Coriander, Anise, Cumin, and Fennel ; but in their case 

 the scent is found chiefly in the fruits, its purpose pro- 

 bably being to keep birds from touching them. Some 

 of these, as well as other scents, like that of Eucalyptus 

 leaves, are used by man as bactericides, or to keep off 

 insects ; others, like Cloves and Allspice, are employed as 

 spices in food to stimulate the taste cells, which, when 

 so stimulated, pour out a larger secretion, and thus 

 make the taste more pronounced. In the plant, such 

 spices are much too strong for a sucking or gnawing 

 insect. Some of them are also exceedingly fatal to 

 bacteria. The vapour of oil of cinnamon kills typhus 

 bacteria in 45 minutes; oil of lavender, or that of 

 Eucalyptus, are also fatal to germs. 



Crystals. — The Sulphur, which is essential for the 

 food of plants, generally enters them in the form of sul- 

 phate of lime. The Calcium, which is eventually set free, 

 combines with oxalic acid, which is formed during the 

 process of assimilation. As oxalic acid is poisonous, this 

 has some importance, but the crystals produced are gene- 

 rally either like long fine needles, " raphidesl' or are 

 rounded bodies covered with hard sharp points. It has 

 been shown (by Stahl) that these crystals prevent snails 

 and slugs from devouring the tissues. Snails even when 

 starved did not touch vegetable tissue full of raphides^ 

 but when these were dissolved by the use of Acetic 

 acid they devoured them greedily. The i^aphides are 

 very common in Monocotyledons. The stalk of the 

 "Arum Lily " i^Richardia ^thiopicd) shows them very 

 clearly. 



Thorns, etc. — Against grazing and browsing animals 

 Thorns, Spines, and Prickles are a much more conspicuous 

 method of protection. Not much is known as to the 

 way in which these are produced ; but in dry climates 



