DEVELOPMENT OF THE FORMS OF CROWN-GALL. 13 



from 9.8 to 33 per cent, or 23.2 per cent. It is also seen that where 

 cuttings were selected from apparently healthy vines in diseased vine- 

 yards some of them (9.8 per cent) became diseased upon rooting. 

 Similar results were obtained by cuttings planted in the soil in a 



vineyard. 



Nearly all of the galls formed on the vines grown from cuttings in 

 the experiment just mentioned were more or less spherical in shape 

 and developed below the surface of the ground, often on the lower 

 ends of the cuttings. 



In structure these root galls are from the first very spongy and 

 watery. They consist at first entirely of parenchymatous tissue. 

 Later there develops in the interior curled and distorted masses of 

 wood cells and vessels, and older galls occasionally become quite 

 woody, especially where they do not die at the end of the growing 

 season. 



The gall develops in every instance, where closely observed, either 

 from an injury to the meristem layer beneath the bark of the cuttings 

 or from a cut surface. An outgrowth of cells first takes place directly 

 from the meristem layer, resembling callus. This develops rapidly 

 into a gall. 



DEVELOPMENT OF CANE GALLS. 



In the cane galls a similar development takes place, but it is not 

 so rapid. Cane galls usually form along a line of injury, often from 

 a wound made in pruning. Very frequently the bark of the canes 

 of grapevines susceptible to frost, such as the Muscat of Alexandria, 

 is ruptured by freezing in the spring after growth has begun. The 

 bark is usually ruptured in longitudinal lines. From the meristem 

 layer in these wounds there develops directly numerous rough galls 

 which are more or less confluent. This gives rise to the form of 

 disease (PI. II, fig. 2) known in this country as black-knot (22) and 

 in Europe as broussins (42), rogna (23), and Grind (15). These galls 

 often become more or less woody in structure. 



The cane galls have been observed as common, with few exceptions, 

 only in localities where vines are subject to frost injury. Where they 

 have been found on vines, all forms of variation have been noted from 

 the spherical root galls of the roots and crowns of the vines to the 

 confluent cane galls on the shoots, indicating that they are both forms 

 of the same disease. 



The cane galls usually dry up in autumn, and may break away from 

 the canes the following season, especially when a further development 

 of galls takes place along their margin. 



183 



