1912.] Summary of Agricultural Experiments. 947 



is the dead zone of the next, and in the following year the dark green 

 inner zone. Measurements of the rates of growth of a few " fairy 

 rings " are given. 



Experiments dealing with the question from various points of view 

 were carried on in both the field and the laboratory, and the 

 conclusions arrived at may be summarised as follows : — 



The fungi investigated are parasites on grass and pasture plants. 

 They attack the young roots, kill them by means of some toxic secre- 

 tion, and gradually destroy the whole plant except the steles. The 

 fungi bring about rapid decomposition of humus in the soil, so that 

 the first effect on the grass is a stimulating one, and there can be 

 distinguished a zone of dark green grass outside the dead grass zone, 

 as well as one inside that ring. 



Infected soil is very impervious to moisture. This is particularly 

 seen in the dead grass zone, which can only with great difficulty be 

 wetted. This was found to be due to air entangled within the meshes 

 of the mycelium. The fungi secrete some substance toxic to themselves, 

 and are not able to grow on the same soil three years in succession ; 

 during the second year the fungus dies off and the grass, gaining the 

 upper hand, flourishes, owing to the increased amount of available 

 nitrogenous food ; hence the well-marked ring of dark green luxuriant 

 grass inside the dead-grass zone. 



It is suggested that the explanation of the well-known fact that 

 "fairy rings" appear only on poor grass land is that on better land 

 the grass is more vigorous and better able to resist the attacks of the 

 fungus. Attempts to start "fairy rings" on lawns or in fields, either 

 by using sods taken from existing rings or by sowing spores of the 

 fungus, were quite unsuccessful. 



A previous note on "Fairy Rings and their Eradication" appeared 

 in this Journal, December, 1907, p. 537. 



Leaf Spot of Celery (Jour. Roy. Hort. Soc, October, 191 1).— 

 Mr. F. J. Chittenden describes a destructive parasitic fungus (Septoria 

 petroselini, var. apii B. and C.) which in 1909 and 1910 attacked celery 

 to a serious extent in many parts of England. Usually the first 

 symptom of the disease is the appearance of small pale spots on the 

 leaves. These are quite unlike the burrows made by the celery fly larva 

 (see Leaflet 35), and on examination with a lens, small, black dots can 

 be seen on them. When the attack is severe, the whole leaf becomes 

 almost olive-green, and soon the foliage wilts and the leaf stalk, which 

 is also attacked, decays. Even when the attack is not sufficiently 

 severe to cause decay, the growth of the plant is interfered with, and 

 the crop diminished. The same fungus also attacks parsley. 



Investigation showed that a great many samples of celery 'seed had 

 the spores of the fungus upon them, and it is suggested that one 

 of the principal ways in which the disease is spread is the use of such 

 seed taken from an affected crop. Where disease makes its appear- 

 ance the affected plants should be removed and burned, and the 

 remainder sprayed with either freshly-made Bordeaux mixture or with 

 a solution of potassium sulphide (1 oz. to 3 gallons of water) repeating 

 the spraying after an interval of about a fortnight or three weeks, 

 and again if necessary. Where disease has existed in a previous year 

 it would be well to commence spraying early in the season as a 

 safeguard. 



3 T 2 



