191 1.] The Perennial or Corn Sow Thistle. 909 



ever, is the only practical mechanical remedy, and should be 

 repeated throughout the summer months, the object being to 

 induce the plants continually to send up new shoots for 

 removal with the spud, thus gradually exhausting the stores 

 of food in the rootstock and preventing the formation and 

 storage of a fresh supply. An endeavour should at the same 

 time be made to improve the general herbage by manurial 

 treatment, and thus crowd out the low-growing thistle. 

 Isolated patches might be dealt with by covering them with 

 large sheets of strong tarred paper, securely fastened down 

 with pegs and large stones. Light is excluded, and all vege- 

 tation beneath the paper is destroyed. The bare spots would 

 need reseeding with grass and clover seeds afterwards. 



The Perennial or Corn Sow Thistle {Sonchus arvensis, L.) 

 attains a height of 2 to 4 ft. ; the stem is tubular and angular, 

 and clothed with yellow sticky hairs in 



Corn Sow Thistle. itS Upper part ; the leaves are wav ^ and 

 toothed, but very variable ; and the 



heads of yellow flowers are rather hairy, and 1 to 2 inches in 

 diameter. It spreads both by seed and by a creeping root- 

 stock. The flowers open in August and September. The 

 Perennial Sow Thistle is a vigorous grower, occurs on most 

 soils in arable land, and may occasion great trouble and 

 damage. Its presence is frequently manifested in corn crops 

 in late summer, when the large yellow flowerheads are very 

 conspicuous. It may be at once distinguished from the 

 Annual species in the mature stage by means of its exten- 

 sively creeping rootstocks and much larger flowers. (The 

 Annual Sow Thistle was described in the Journal in June, 

 1909, p. 207.) 



In order to combat this weed, seeding must be prevented 

 by cutting the plants just before they reach the flowering 

 stage. During the summer the plants manufacture a large 

 amount of food-material in their leaves, and this is trans- 

 ferred and stored below ground in the roots and root buds. 

 To cut off the stems of this pest after this storage has taken 

 place has no exhausting effect on the crop, and cutting once 

 or twice late in the season can be practised for years without 

 diminishing its vigour. To cope with the Corn So-iv Thistle it 



