204 THE MONTHLY BULLETIN. 



growth affects the rapidity of gall formation. If there is no growth of 

 tree there is little or no development of gall. Iiioculation late in 

 the fall often ivill not develop until active growth the following spring. 

 May not this retarded development of the disease account for the large 

 amount of gall that sometimes develops on young orchard trees from 

 stock that was carefully inspected and appeared to be perfectly free 

 from crown gall? 



AVENUES OF ENTRANCE. 



Crown gall infection must start from soil containing the disease- 

 producing organism. There can be little doubt but that the soils of 

 California are often naturally infected with crown gall. This is 

 especially true of those that were formerly wooded or have previously 

 grown stone fruits, especially if the latter were on peach roots that 

 were infected with gall. 



Little is actually known as to how actively the disease spreads under 

 nursery irrigation. The fact that irrigation increases the amount of 

 crown gall would suggest that the disease is possibly spread in this way. 



On vigorous growing seedlings like almonds, there is often a scar 

 directly beneath w^here the seed is attached that would be a most favor- 

 able place for gall infections. Almond seedlings also sometimes show 

 small checks or cracks in the surface bark. The gall usually appears at 

 the crown and very close to where the seed was formerly attached. 

 Some experimental work is in progress in treating pits before planting 

 with a thick paste of Bordeaux mixture with the hopes that possibly 

 this wdll sterilize a small area of soil immediately surrounding the pit 

 and so possibly prevent this early infection of the tree. These experi- 

 ments, however, did not lessen the amount of gall as compared with 

 other check trees. 



Any injury to the trunk or root in the nursery or in digging the trees 

 would be a favorable point for infection. The organism is entirely a 

 wound parasite and could gain entrance in any mechanical injury, 

 animal or insect bites. 



HOSTS. 



The following is a list of plants upon which crown gall has been found 

 to occur naturally: Apple, apricot, almond, Arbutus unedo, alfalfa, 

 beet, clematis (wild), clover (red), cherry, chestnut, cotton, daisy 

 (Paris) or marguerite, grape, hop, honeysuckle, loganberry, peach, 

 pepper tree, plum, prune, pear, parsnip, pecan, quince, raspberry, rose, 

 salsify, stereulia, Victoria bottle tree, turnip, willow, English walnut, 

 California black walnut, eastern walnut. 



Galls have been artificially produced on the following in addition to 

 those named above : Catalina cherry, eucalyptus, citrus, sweet orange, 

 sour orange, lemon, lime. Anglers quince, Japanese walnut, butternut, 

 a large number of different species of cultivated and wild plums, includ- 

 ing the following : Primus cerasifera, P. Americana, P. triflora, P. domes- 

 tica (some of these varieties are quite resistant) ; P. amygdalus, 

 P. Armenica, P. avium, P. davidiana, P. hortnlaita (wild goose), 

 P. Allegheniensis, P. Simonii, P. platycarpa, P. myra, P. eriogyna. 



