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ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 



and many other cultivated and wild 

 plants, herbaceous as well as woody. It 

 is very common on members of the rose 

 family (Rosaceae) to which all of our 

 ordinary tree fruits and many of our 

 small fruits belong. Besides the plants 

 above mentioned, it is reported as at- 

 tacking the grape, walnut, chestnut, pop- 

 lar, willow and alder. In the North- 

 west it is known on practically all of 

 our tree fruits, is found on blackberries, 

 raspberries, loganberries and grapes, and 

 also on the hop. The usual effect upon 

 these different hosts is the production 

 of tumors or galls, which are in general 



Fig. 1. A, Crown Gall on the Canes of Grape. 

 B. Crown Galls on the I'each Root of a 

 Prune Tree. C, Crown Gall on a Loganberry 

 Root. 



somewhat similar in form and appear- 

 ance. The galls, as a rule, have an an- 

 nual development, that is, they begin to 

 form in the spring as the tree starts 

 active growth and cease development in 

 the fall. At first they are small, nearly 

 spherical masses of more or less suc- 

 culent tissue, whitish or translucent in 

 appearance but rapidly becoming darker 

 and uneven, till at maturity they are 

 dark brown and warted. When occur- 

 ring on small roots they may be only 

 about one-quarter inch in diameter, while 



on nursery stock, raspberries, etc., they 

 may be about the size of a walnut. On 

 large trees in the orchard they may 

 reach a much greater diameter. The 

 galls usually occur at the base of the 

 trunk or on the roots, though in some 

 plants they are found on the stems or 

 branches above ground. The most com- 

 mon point of attack, howeyer is just 

 beneath the ground at the crown of the 

 plant. A peculiar form of the disease 

 known as hairy root occurs commonly 

 on the apple. 



The effects of an attack of this dis- 

 ease are much more serious on certain 

 kinds of plants than upon others and 

 even among individuals of the same kind 

 there are wide variations in the result- 

 ing amount of damage. In some cases 

 trees may be affected without giving any 

 signs of harmful effect upon growth or 

 production of fruit. In other cases, trees 

 or smaller plants are often stunted and 

 unprofitable and not infrequently die as 

 a result of the presence of the galls. 

 There are also many well-authenticated 

 instances where trees known to be bad- 

 ly affected with crown gall have exper- 

 ienced apparently complete riecovery. 

 Furthermore, some of the serious ill ef- 

 fects attributed to this disease must of- 

 ten, on careful investigation, be charged 

 to other troubles which have had entrance 

 through the unprotected or decayed gall. 

 The fire blight bacteria, mushroom root 

 rot. wound parasites and heart rot fungi 

 of various sorts as well as certain insects 

 have easy access to a tree through galls 

 where a healthy bark would have pre- 

 vented any attack, and in most cases 

 these secondary intruders are liable to 

 have more serious consequences for the 

 tree than the mere presence of the gall. 

 It is supposed also that the disease may 

 appear in severe or in light form, depend- 

 ing upon the virulence of the strain of 

 organism producing the infection. 



The detrimental effect of the crown gall 

 itself may arise in several ways. The 

 tumors rob the plant of some nutriment. 

 Excessive evaporation of moisture may 

 occur from the unprotected gall surfaces, 

 especially where aerial galls are abund- 



