30 AgricuJturaJ Kjcpcrimoit Station Ue.search Bulletin 1\ 
'svere oTowiii^’ in soil that had l)eoii inocailated with the cowpea or 
with the soy bean strain of Fusarium. 
EXPERIMENTS ON THE RELATION OF VARIOUS SOIL FACTORS TO 
INFECTION OF SOY BEANS BY F. TRACH El PH I LU M 
THE INFLUENCE OF SOIL TYPES 
Since artilicially inocnlated soy beans have not always 
developed the disease, nor developed it to the same degree of 
severity that cowi:>eas have under the same conditions, nor as 
severely as naturally infected soy beans in the field, a number of 
experiments were planned to determine the factor or factoi’s 
which seemed to be responsible for the limitations. At the outset 
possiblv all of the factors of the air and soil that influence the 
health of plants might be concerned. The effects of certain of 
these have been under consideration in the following experiments 
in which, with the exception of that on Norfolk soils, all of the 
plants were subjected alike to those factors which it was impossi- 
ble to control. In this way evidence Avas obtained as to the effect 
produced by certain factors by ATirying one, nnder control, in 
each experiment. 
The relation of conditions above the ground, such as tem- 
perature, humidity, and light, to the snsceptil>ility of })lants to 
])arasitic diseases is often an important one, but a study of them 
in connection Avith the disease at hand has not yet been made 
because a more direct relation ])robably exists betAveen soil fac- 
tors and infection. In consideration of the soil, attention has 
first been gi\Tm to the effect of A’ariation in texture Avhich is 
limited by the size of soil ])articles and by organic and inorganic 
materials Avhich further influence such factors as temperature and 
Avater holding capacity. The United States Bureau of Soils has 
divid(‘d soils into tyj)es, classes, and series. 
Soil class — “Soil types, Avhich constitute the units of soil 
classilication, may be grouj)ed in dilferiMit Avays. As M)ils aiv 
made up of ])ai*ticles of difl'ercMit sizes, tluw may be grouped 
according to the relative* proportions of the |)articles of dilf(*rent 
siz(‘s Avhich they contain. I'his grout)ing is knoAvn as soil class 
and is bas(‘d on t(‘Xture." (30. p. It).) 
Soil series — “It has 1h‘(*u found that in many parts of the 
United State's a give'ii^ se*t of soil elasse's are se) evidently relateel 
thru source* of mate*rial, m(*the)d of formatie)U. topographie* i)osi- 
tion and e-oloratiou that dilh*re*nt tyj)e*s eonstitute* me*re*ly a grada- 
tion in the* te*xtiire* of an othe*rwise* unife)i*m mate*rial. Soils e>f 
dillere'ut e’lasse*s that are* thus i’e*late*d e'onstitute* a se*ries. A com- 
ph*t(* soil se*ri(*s consists of mat(*rial >imilar in many other charac- 
