INSECTS WHICH PREY UPON AGPJCULTUEAL PLANTS. 109 



" shield," or rough leathery patch on the anterior part of the 

 back. The eyes are fixed at the extremity of the retractile 

 horns, and may be seen by the naked eye as little black specks. 

 The aperture on the right side forms the " breathing sac," — tak- 

 ing the place of the luncjs of hidier animals — and oenerative 

 opening. Snails and slugs are hermaphrodite, each individual 

 thus laying eggs. These eggs are found under stones, and at 

 the roots of grass, as clusters of little white pellucid bodies like 

 sago in appearance. 



Limax ater is the large black species. There are scarcely 

 any more destructive pests than these two creatures, and no 

 kind of crop comes amiss to them. Troops of ducks are a capital 

 cure if driven over the affected crop in the evening or after rain, 

 and a dressing of lime or soot put on when the leaves are wet, 

 renders them unpalatable, if not deadly to them. 



Vibrio tritici This creature, which belongs to the Infusoria, 

 is the cause of the disease known as " purples," or " earcockle " 

 in wheat. The affected grain assumes a purplish-black colour, 

 and becomes rounded in appearance ; if one be taken and opened, 

 the inside will be found to contain a cotton-like substance, into 

 which the original starch, &c., has been changed. In this bed 

 will be found a number of microscopic eel-like animalcules, 

 which readily separate in warm water. When an infected grain 

 is sown, the vibrios make their way from it to the sound stalks, 

 which they gradually ascend until they reach the ovules, where 

 they make their nidus, dejjosit their eggs, and die. As the 

 diseased grains are light, winnowing will separate them. , 



There are, of course, many more insects which infest farm 

 crops at home and abroad, but the above-described kinds com- 

 prise the most conspicuous and troublesome of them that are 

 found in this countrv. 



In conclusion, a few general remarks may be offered on the 

 manner of coping with these tiny enemies. ^lostly all insects 

 delight in moisture, so that draining is prejudicial to them, while 

 beneficifd to the soil and crop. When laud is broken up for the 

 first time the practice of paring off and burning the turf and 

 rubbish is sometimes carried out, thereby killing the "grubs" 

 and wireworms hiding therein, and the good crops often seen 

 after this operation are partly due to their freedom from insect 

 injuries. Many of the weeds belong to the same natural orders 

 as our crops, and are thus suitable for food tn insects when there 

 is nothing else, so that these should bo kept down. Early 

 ploughing and autumn cultivation fur the purpose of exposing 

 the soil to the actiuii of the frost is a good }»lan, as many are 

 thus killed. All our feathered songsters are insectivorous, and 

 should therefore be encouraged. When a crop is growing, dress- 



