222 Diseases of Greenhouse Crops 



soaked and possess no watery margin. They are 

 always sunken, and possess no definite center. The 

 cause of the trouble does not seem to be associated 

 with any parasitic organism, but is probably due to 

 improper cultural conditions, the exact nature of 

 which is unknown. 



Control. The control for yellows, as recom- 

 mended by Peltier"^ is as follows : Every check which 

 tends to lower the vitality of the plant should be 

 avoided. Weaker plants are more subject to yellows 

 than stronger ones. Cuttings should never be taken 

 from plants showing yellows. They should be made, 

 too, from plants in bloom rather than from stock 

 plants. They should be rooted early and should not 

 be permitted to remain too long in the sand after 

 rooting. The later the cuttings are made, the longer 

 they take to root, and the more susceptible they 

 are to yellows. Young plants should not be allowed 

 to become pot bound. 



Cohesion of Petals 

 Cause unknown. 



Carnation growers are often troubled by what is 

 generally termed cohesion of petals. The latter are 

 well out of the calyx, but are stuck together. Often 

 they are grown together to such an extent that it is 

 impossible to separate them without tearing the 

 tissue. The trouble was first described by Arthur,t 

 but the exact cause of it is as yet unknown. 



♦Peltier, G. L,, The American Flor. 46: 725-726, 1906 

 t Arthur, J. C, Proc. Amer. Carnation Soc, 1896. 



