DISEASES OF CULTIVATED PLANTS 625 



fected soil lies in the discovery of some variety of tobacco that will 

 not wilt even when planted upon sick soil. Varieties of cotton that 

 can resist the cotton wilt, and of cow peas that can resist the cow-pea 

 wilt have been discovered. There is similar hope in regard to the 

 tobacco wilt. If several plants grow under the same conditions in 

 infected soil and one of them survive while the others wilt, this sur- 

 vival may be due to a special resistance on the part of the plant 

 which prevents the encroachment of the parasite. Such a plant 

 should be caused to seed, and its seeds saved with great care, since 

 this ability to resist the disease is a character that may be transmitted, 

 to the plant's offspring. Seeds from resistant plants should be tested 

 on sick soil, and any plants that prove resistant should again be 

 saved as seed plants. A few years of such selection of seed from 

 resistant plants may result in the development of a race of wilt- 

 resistant tobacco similar to the wilt-resistant cotton and cow peas, 

 which were developed in a similar manner. (N. Car. E. S. B. 188.) 



DISEASES OF FLOWERS. 



BEGONIA. 



Nematodes. These minute worm parasites attack the roots and 

 also the leaves of cultivated begonias. For the commoner root in- 

 jury avoidance is to be sought in the preparation of the earth. 



Root-Rot. The root-rot fungus of violets and tobacco (Thiela- 

 via basicola) was found attacking the roots of begonia which suf- 

 fered from nematodes. Its general occurrence since the discovery 

 upon tobacco and catalpa show that it is capable of serious injury to 

 the roots of these cultivated plants. (Ohio E. S. B. 214.) 



CARNATIONS. 



Carnation Disease. It generally starts in the leaf when im- 

 mature, and is best diagnosed in the younger 'but full-sized leaves 

 nearest the upper end of the stem. Taking such a leaf, which on its 

 surface presents no unusual appearance to the eye, and holding it 

 toward a strong light, small, pellucid dots may be detected scattered 

 irregularly through the leaf, sometimes having a faint yellowish 

 color, which are the centers of infection. The appearance of the 

 dots has a close resemblance to those of the oil glands in the leaves of 

 the common St. John's wort (Hypericum perforatum) , a rather 

 abundant weed, or in the leaves of the false indigo (Amorpha fruti-* 

 cosa) , a native shrub, except that they have no regular disposition. 

 Sometimes the surface of the leaf is slightly raised over the dots, 

 making watery pimples. 



After a time the surface of the leaf above the dots changes 

 enough to indicate their presence and finally shows a distinct spot. 

 As the disease extends inside the leaf the surface tissues dry, the in- 

 ternal tissues collapse, and whitish, sunken spots appear. In some 

 colored varieties of carnation the spots vary somewhat by being 

 more or less reddish or purplish. As the spots increase in size the 

 leaves wither, still clinging to the stem. Such spote never show 

 distinct central darker-colored specks and rarely any concentric 



