28 



Jiast Mailing Research Station, and the Ministry is indebted 

 to Mr. N. H. Grubb of that station for the notes given below 

 on English fruit stocks. 



Description of the Disease. In its typical form Crown 

 Gall manifests itself as roughly spherical swellings which may 

 vary in size from that of a pea to that of a cricket ball. The 

 galls are at first white and soft, but gradually become hard and 

 dark in colour. On nursery stock they often decay and fall 

 away at the end of the season. Hedgecock has distinguished 

 the more woody perennial form usually found 011 older trees 

 as " hard crown-gall." These are slower growing, but continue 

 to enlarge for many years and become very hard. On old 

 plum trees very large galls, 8 or even 10 inches in diameter, 

 may sometimes be found. 



The position of the swelling also varies considerably. As 

 the name implies the galls are often found at the crown or 

 collar of the attacked plants, but they may occur on the roots 

 or on the stems and branches. The latter is the usual form in 

 raspberries. Where root-grafting is practised they are particu- 

 larly frequent at the junction of the stock and scion. 



In the case of apples it is found at East Mailing that in 

 stocks raised from layers or stools, by far the largest propor- 

 tions of galls occur on the base of the stem at the point where 

 it was separated from the parent stool or layer. Infections 

 higher up the stem are sometimes found and others on lateral 

 roots, but galls at the ground level, or " crown *' of the stock 

 are rare. The galls on these stocks usually take the form of 

 rough warty swellings of soft tissue which vary in development 

 from a slight irregularity of the " callus " to large, more or 

 less spherical galls up to three or four inches in diameter. 



A form very different in appearance is frequent in America 

 and is known as " Haify Root " (see Fig. 3). In this case 

 dense tufts of fibrous roots are produced on various parts of 

 the root system. These have been found to be caused by the 

 same bacterium as that causing Crown Gall, the bacteria being 

 found in the flattened tumours on the main root from which 

 the tuft of fibres arises. Various types of Hairy Root have 

 been recognised, but in this country, though suspicions cases 

 Have been observed, no instances have been seen which can 

 with certainty ^6e referred to that disease. 



Method of Attack. It has been proved by direct inocula- 

 tion and other experiments that the bacteria gain entrance 

 through wounds and in all probability they cannot enter an 

 uninjured surface. This has been confirmed by trials in nur- 

 series where plants intentionally wounded gave rise to four 

 times as many galls as those not so treated. It is well known 

 also that seedlings are less often attacked. In the case of 

 cuttings and root grafts the period during which the plants 

 are vulnerable is jnst prior to and during t-be formation of the 

 callus. 



