248 INSECTS, DISEASES AND OTHER PESTS 



A third form may be mentioned here, which is found 

 only on the red flowered varieties, as Beacon. Here 

 the areas in the late stages take on a purplish color and 

 are slightly raised. It is not known whether this form is 

 the same as the others or not. The red flowered varieties 

 are susceptible to both types. 



As new shoots arise they become infected, while the 

 old leaves at the base of the plant die off, giving the plant 

 a very diseased appearance. While yellows does not kill 

 the plants outright, it renders them useless, for they will 

 produce only a few imperfect flowers, and in only slight 

 attacks of yellows it retards the growth of the plant. 



Microscopical observations show no rupture of the 

 epidermis and with a lens the bloom on the leaf above 

 the spots appears to be undisturbed. The chloroplasts 

 are lighter in the diseased areas but do not seem degenerated. 

 No bacteria or fungi are present except when the epidermis 

 of the leaf is broken down. No insect punctures, as have 

 been described by Woods, have been observed in the true 

 yellows, in fact no collapsed tissue can be traced to the 

 epidermis except in later stages, when the epidermis has 

 been broken down. 



No explanation as to the cause of this disease can be 

 given at present. However, preliminary experiments 

 have shown that the disease is probably not transmissible 

 from one plant to another, but that it is carried from season 

 to season by means of infected cuttings. Until the cause 

 has been determined the suggestion is made that no cuttings 

 from plants that show yellows be taken; and if any plants 

 show these spots at any time from the cutting bench stage 

 to the time they are brought into the house in the Fall 

 they should be discarded. In this way the disease to a 

 large extent will be eliminated. 



