56 CAUSE AND NATURE OF CROWN-GALL 



tres. From its parasitic habit and custom of fruiting under 

 ground, it has become degenerate and differs materially from 

 the saprophytic species. In the character of the sporangia and 

 color of the spores, its affinities are with the T) ichiacccc, as de- 

 fined by Schroter. 41 It differs materially, however, from the 

 Trichiacecv in having a poorly developed capillitium ; but it is 

 likely that this organ has degenerated and is gradually disap- 

 pearing, as it can serve in no possible way in the dissemination 

 of the spores. 



HOW THE DISEASE SPREADS. 



The widespread dissemination of the disease has arisen by 

 infested nurseries sending trees into many widely separated re- 

 gions. A single nursery may be the means of spreading the 

 disease over an entire State or over several States. 



An orchard with a comparatively small number of diseased 

 trees at time of planting will usually have few perfect trees re- 

 maining after the expiration of several years. This is particu- 

 larly true of orchards in irrigated regions on account of the 

 contagion being carried from tree to tree at times of irrigating. 

 In the Glendale orchard some of the trees were diseased when 

 planted. The actual number, however, that had galls upon 

 them was very small. After the expiration of eight years less 

 than i per cent, remained unaffected. 



The conclusion seems to be warranted that the contagion can 

 be carried in the old, decayed galls as well as in the fresh tissue. 

 The spores are so small they can readily be carried by the wind. 

 The amoeboid bodies elsewhere described are particularly adapted 

 for carrying in water. The decayed galls which break from 

 the tree from time to time may be carried about by the culti- 

 vator. If the bark at the crown or on surface roots be broken 

 in cultivating, even on old trees, it gives the disease an oppor- 

 tunity to become established. Trees that are closely pruned 

 frequently sucker at the crown, and as the young sprouts break 

 through the bark an entrance is available for the parasite. 



41 Die Natiirlichen Planzenfaniilien, Engler and Prantl, Teil. I, Abt. 

 i, p. 20. 



