200 THE PRINCIPLES OF FLORICULTURE 



STUDY OF DISEASE-PRODUCING PLANTS IN THE 

 DIFFERENT GROUPS 



.To understand better the general character of fungi which 

 cause plant diseases, their methods of attack, also methods of 

 prevention and extermination, a general consideration of the 

 more important disease-forming plants follows : 



168. Myxomycetes (slime-fungi). There are few disease- 

 forming agents in the Myxomycetes. They attack root tissue, 

 forming a malformation, and therefore an abnormal growth. 



169. Schizomycetes (Bacteria) : 



(1) Stigmonose of carnations : Stigmonose of carnations is 

 now believed to be a disease which originates where fumigation 

 has been neglected* The soft, succulent tissues of carnations 

 are punctured by insects, and bacterial colonies gain entrance 

 through these injuries. A breaking down of the leaf or stem 

 tissues results. Keeping plants free from insects, and having 

 atmospheric and soil conditions conducive to healthy growth, 

 will assist greatly in keeping this disease in check. 



(2) Bacterial difficulties in bulbs : Many bulbous plants, such 

 as lilies, hyacinths and tulips, are frequently attacked by bac- 

 teria. Frequently, bulbs are harvested before they are mature, 

 and become more or less bruised in shipping. Therefore, the 

 bulbs are more susceptible to bacterial attacks. Care should 

 be taken in buying bulbs, to secure only those with healthy, 

 well-ripened tissue, and which show no indication of the presence 

 of disease. 



170. Phycomycetes (Algal fungi). " Damping-off " fungus. 

 Classification : Phycomycetes, Pythiaceae. Pythium deBaryanum. 

 The " damping-off " fungus is the chief representative of the 

 Phycomycetes which is of interest to the growers of orna- 

 mental plants. It is common in seed beds and cutting benches 

 and causes a rapid loss of seedlings and cuttings. It attacks 

 plants near the ground, and they quickly fall, the top remain- 

 ing green for some time after the stem has blackened. Inves- 

 tigation shows the root to be badly decayed before the top 

 reveals the effects of the disease, the moist atmosphere giving 

 the top sufficient moisture to sustain life. The progress of 

 the disease is rapid if the atmospheric conditions are in its 

 favor, and a whole seed-pan may become diseased in a single 

 night. The fungus naturally lives as a parasite on living plants, 

 but it may exist on decaying vegetable matter and then becomes 

 saprophytic. 



