DISEASES OF PLANTS. 249 



common greenhouse diseases of tomatoes, lettuce, chrysanthemums, and 

 carnations can also be controlled if the proper moisture, heat, and light condi- 

 tions are present. 



Malnutrition, G. E. Stone {Massachusetts Sta. Rpt. 1909, pt. 1, pp. lo.'f- 

 i62).— Several cases of malnutrition in plants are recorded, due principally, it 

 is claimed, to injudicious use of commercial fertilizers, especially in greenhouses. 



Malnutrition in cucumbers grown under glass is very common, and is char- 

 acterized by a rolling of the foliage producing a convexity of the upper surface 

 of the leaf, while the margins of the leaf are usually slightly burned or dead. 

 The addition of pig, cow, hen, and sheep manures, nitrate of soda, or other con- 

 centrated fertilizers to an already sufficiently fertile soil is claimed to be the 

 cause of the malnutrition. 



Calico or mosaic disease of cucumber and naelon, G. E. Stone {Massachu- 

 setts Sta. Rpt. 1909, pt. 1, p. 163). — Attention is called to the occurrence of this 

 disease in cucumbers and melons grown under glass. The trouble is character- 

 ized by a mottled appearance of the foliage, and the whole plant appears 

 abnormal. 



A similar spotting and mottling occurred on pruned tomato plants. 



Field studies of the crown gall and hairy root of the apple tree, G. G. 

 Hedgcock {V. 8. Dept. Agr., Bur. Plant Indus. Bui. 186, pp. 108, pis. 10).—^ 

 The results are reported of several years of investigation and experiments on 

 crown gall and hairy root, including descriptions of their different forms, their 

 probable relations, their development, their effects on apple trees, the suscepti- 

 bility of different varieties, infection in the nursery and orchard, and means 

 of control. 



As a result of these investigations it was found that crown gall and hairy 

 root occur in nurseries and orchards throughout the apple growing regions of 

 the United States, and has been reported in Europe, South Africa, New Zealand, 

 and Australia. There are two forms of the crown gall on apple trees, the soft 

 and the hard. A similar crown gall is also found on the almond, apricot, black- 

 berry, cherry, chestnut, grape, peach, pear, plum, prune, raspberry, rose, and 

 walnut. 



The hairy-root type of the disease may occur in four forms, as follows : The 

 simple form, characterized by numerous roots springing at right angles from a 

 large root; the woolly-knot form, composed of numerous more or less parallel 

 roots springing from a hard gall on a longer root; broom root, a side root with 

 much fasciated, fine branch roots, often negatively geotropic; and aerial galls, 

 which are the woolly-knot form on the limbs of the trees. All these forms of 

 hairy root are probably directly related to the forms of crown gall. 



The soft form of the crown gall is most common on yearling apple seedlings, 

 and is occasionally found on budded and root-grafted trees. The hard form is 

 common on budded trees, and much more abundant on root-grafted ones. 

 Hairy root of the simple form is frequent on apple seedlings and on budded and 

 root-grafted trees, while the woolly-knot form is the most common form of the 

 disease, esi3ecially on 3-year-old root-grafted trees in the nursery and on orchard 

 trees. 



Crown gall gains entrance almost entirely through wounds. Heavy, stiff, 

 clayey, wet soils apparently increase the amount of crown gall, especially in 

 nursery stock. 



Orchard experiments indicate that older apple trees in many cases success- 

 fully resist both hairy root and crown gall, and that many may completely 

 recover. Experiments also indicate that the effect of crown gall and hairy 

 root upon apple trees in the orchard has been overrated, at least in the estab- 

 lished apple regions of the Central and Eastern States. 



