cluding parasitic agencies, such as fungi, bac- 
teria, viruses, and animals; and nonparasitic 
factors, such as unfavorable environment and 
improper nutrition. In this discussion we will 
consider only parasitic diseases. 
1. FUNGI. Common examples of diseases 
caused by fungi are blackspot and mildew of 
Rose, rust and Alternaria blight of Carnations, 
verticillium wilt of Chrysanthemums and 
dozens of others. 
Fungi are low forms of plant life which are 
unable to carry on photosynthesis. Many spe- 
cies are beneficial in that they decompose only 
now living organic materials. The parasitic 
species which obtain their food from living 
plants and in doing so injure the plants are 
the ones which cause disease. 
Fungus material consists primarily of 
threads called mycelium. The mycelium 
grows between and through plant cells, de- 
stroying the cells and thus causing disease. 
Most fungi produce spores which are compar- 
able to seeds of higher plants. The method of 
spore production varies greatly in different 
species of fungi. Spores may form either on or 
in the mycelium or may be produced in special 
structures or fruiting bodies. The method of 
spore production; spore size, shape and color; 
and the characteristics of the mycelium are 
used as a basis to classify fungi into genera 
and species. 
Fungus diseases are disseminated in various 
ways. Spores may be distributed by splashing 
water (blackspot of Roses during syringing). 
The spores may float in air currents (Rose mil- 
dew). Spores and mycelium may be carried on 
or in seed, bulbs, cuttings, etc. (Aster wilt, 
Tulip fire). Infested soil isa common means 
by which disease carries over from one crop 
to the next. | 
Environment, particularly as it relates to 
temperature and moisture, influences the de- 
velopment of fungus diseases just the same 
as it influences the growth of higher plants. 
Spores will not germinate and cause infection 
except in the presence of sufficient moisture 
and within a certain temperature range. Most 
fungus diseases will develop under the moisture 
and temperature conditions favorable for the 
host plant but by properly controlling tem- 
perature and humidity in the greenhouse dis- 
ease development can be greatly retarded. 
The control of environment and strict atten- 
tion to sanitation rank high as disease control 
measures in any floral establishment. 
2. BACTERIA. Crown gall, soft rot of 
Calla Lily, bacterial blight of Carnation, fasci- 
ation of Sweet Pea, Chrysanthemum and some 
other plants, scab of Gladiolus are common 
examples of diseases caused by bacteria. 
Bacteria are like fungi in that they cannot 
carry on photosynthesis. 
They are extremely small, single celled or- 
ganisms, although some species occur in chains 
or clumps. An average sized bacterium would 
be about .5 by 1.5 microns. A micron is 
.000039 inches. Bacterial cells may be spheri- 
cal or short rods. They may be motile or non- 
motile. Some species, such as the crown gall 
organism, will cause disease in many different 
species of plants; whereas others will attack 
only certain varieties of a single species. 
They are transmitted on tools, in soil, by 
splashing water, and on plant parts. 
Infection occurs through wounds and fre- 
quently through stomata. Abundant moisture 
is necessary for infection to occur. 
The bacteria grow between and in the plant 
cells, either killing the cells or stimulating 
them to abnormal activity and thus cause 
disease. 
3. VIRUSES. Mosaics of Stocks, Sweet 
Pea, Lily, Dahlia, Rose; breaking of Tulips; 
crinkle of Geranium; and Aster yellows are 
examples of virus diseases. 
Virus particles are ultramicroscopic in size, 
lying in the region between 250 to 10 milli- 
microns (a millimicron is 1/1000 of a micron). 
Only a very few viruses have been isolated in 
the pure state and they have been found to 
be proteins. 
Viruses are transmitted in cuttings and bulbs 
but very seldom in seeds. In some instances 
they are transmitted by merely handling 
plants. Sucking insects, such as aphids and 
leafhoppers are common transmitting agents. 
4. ANIMALS. In this class we will consider 
only nematodes, although certain other ani- 
mals may cause a disease condition in plants. 
Nematodes are microscopic eel worms. Some 
species infest only the roots of plants, whereas 
others attack only foliage. They will live in the 
soil for a fairly long period of time even though 
susceptible plants are not present. 
In this state nematodes are usually killed by 
freezing during the Winter if they are free in 
the soil out of doors. They survive freezing 
temperatures when they are inside of roots, 
such as Peony, Rose, Clematis and others. 
They are eliminated from soil by steriliza- 
tion, heat and certain types of chemical 
treatments. 
“Commercial Flower Foreing’’, a most 
valuable book of helpful information for grow- 
ing nearly all plants and flowers in green- 
houses. 
