DISEASES OF PLANTS. 53 



the roots, but more commonly by contact, as in handling plants, etc. The dis- 

 ease is carried by seed to a limited extent, insects may spread it, but infected 

 platits in the seed bed are believed to be the primary source of the trouble. The 

 genuine disease is not developed by pruning if it is not already present or intro- 

 duced during the pruning process. 



Calico is said to require 10 to 14 days after infection before the disease 

 becomes apparent. The extent of development depends on the age of the plant 

 at the time of infection, mature leaves not being visibly infected, although they 

 may serve as carriers of infection to younger ones. 



A similar disease of tomatoes is recognized, and it was found possible to recip- 

 rocately inoculate tomatoes and tobacco, causing the characteristic appearance 

 of the disease. Other species of Nicotiana were successfully inoculated, as were 

 a number of other solanaceous plants, but not of plants belonging to other plant 

 families. 



The " virus " is said to be renewed within the tissues of the plant, is destroyed 

 by heat, is filterable, can be extracted with alcohol, ether, and chloroform, and 

 retains its vitality for some time in the presence of toluol. The author considers 

 the " virus " as being of the nature of an enzym, and the experiments are be- 

 lieved to suggest that it belongs to the group of oxidizing enzyms. 



Bacteria are not considered as causing the trouble here described. 



Suggestions for the control of the disease in the seed bed and field are given. 



A bibliography of some of the more important contributions to the subject of 

 plant chlorosis is given, in which brief abstracts of the subject matter are 

 included. 



New tomato diseases, R. Rapaics (Ahs. in Bot. Centbl., 126 (1914), No. 23, 

 p. 625). — The author reports, at Debreczen, Fusarium erubescens as causing a 

 dangerous disease of ripe or unripe tomato fruits, CoUetotrichum lycopersici as 

 causing anthracnose in mild form on the unripe fruits, and Septoria lycopersici 

 on the leaves. 



Note on E-hizopus nigricans, H. Woemald [Jour. Southeast. Agr. Col. Wye, 

 No. 22 (1913), pp. 483-4SG, fig. 1). — Study of the organism causing a rot of 

 tomatoes showed by comparative tests that the strain from Kensington and that 

 from Wye are to be regarded as plus and minus, respectively. 



Watermelon wilt spread by contaminated seed, H. R. Fulton and J. R. 

 Winston (North Carolina Sta. Bien. Rpt. 1913-14, pp. 48-51, fig. i).— Attention 

 was called in August, 1912, to a destructive melon disease due to Fusarium 

 niveiwi. Observations indicate that, while the disease was widespread, it seemed 

 to be associated with one lot of seed as the source of infection. Seed of this lot 

 were procured, and upon germination, showed the presence of the fungus F. 

 niveum. Pure cultures were obtained and the disease readily produced by in- 

 oculation experiments. 



When infected seed were disinfected no disease appeared on germination, indi- 

 cating that the seed were only externally affected. Some experiments in disin- 

 fecting seed were carried on which indicate that soaking seed for 30 minutes 

 in 0.5 per cent solution of formaldehyde not only increased the germination of 

 the seed, but also greatly reduced the infection. 



Wood decay in orchard trees, W. T. Horne (California Sta. Circ. 137 (1915), 

 pp. 13, figs. 2). — Attention is called to the frequent occurrence of rots affect- 

 ing orchard trees, in some instances apple and stone fruit trees being seriously 

 attacked. The decay is said to be due to wood-destroying fungi, and serious 

 losses have been reported from a number of localities in California. 



The author recommends cutting out, disinfecting, and coating the wounds 

 with asphaltum. The trees should be inspected at the end of the summer and 

 the disinfection renewed if necessary. 



