Vol. XXV, No.' ii 
438 Journal of Agricultural Research ' 
which the young sprouts pushed through the soil in response to the tem¬ 
perature of the soil. With the pea, in the unsterilized soil of Experi¬ 
ments 1 and 2, the plumules were destroyed only at temperatures 
approximating the apparent optimum for tissue destruction (15 0 to 
21 0 C.). In Experiment 3, however, under conditions more favorable 
for the pathogenic action of the fungus, growing-point injury occurred 
at 28°. Nevertheless, even under these severe conditions such injury was 
limited primarily to temperatures below 20°. As in the case of the 
potato, it appears quite probable that the rapid growth after germination • 
played an important part in the protection of the plumules at the higher 
temperatures. 
Normal pea growth was obtained throughout the entire range of 
temperatures of from 9 0 to 29 0 C. (PL 1, A). However, the most rapid 
germination and early growth, indicated by the time at which the plants 
appeared through the soil, occurred at 28° and 29 0 . 8 These results 
agree essentially with the optimum secured by Leitch (10). Dry-weight 
determinations showed the greatest growth of the normal plant for a 
period of sixteen days at 21 0 C. (Fig. 2 and Table IV.) Were the dry 
weights taken as an index to the temperature values at this period of 
the plant growth, it is clearly evident that the optimum for germination 
and early growth and the optimum for the later development of the 
plant would be widely different. This same relation was shown to 
exist for the potato under similar experimental conditions (jj). 
TEMPERATURE STUDIES WITH THE BEAN 
Studies with the pea and the potato show clearly a similar soil tem¬ 
perature range for the pathogenic action of Corticium vagum on these 
two hosts. With both these plants 18 0 C. appeared optimum for tissue 
destruction. It will be recalled further that 18 0 approximates closely 
the soil temperatures found most favorable for the later and continued 
growth of both the pea and the potato. Whether this temperature 
relation between parasitism and host development is merely coincident 
with the two plants, due possibly to their similar temperature require¬ 
ments for growth, or whether it is a condition determined primarily by 
a fixed character of the pathogen, does not appear clearly from the data 
obtained: Such data las Jones has v supplied on cotton (Table I, fig. 1) 
support the latter possibility. However, to settle this question, additional 
experiments ^ith other plants having temperature requirements different 
from either the pea or ,the potato appeared necessary. The wbfk affd'ob- 
servations of Reynolds (12) , Reddick (j/), Barrus (4)', and'JBiirkholddr (6) 
on the relation of temperature to the growth of the ‘bean* suggested this 
plant as a favorable host for this additional study.' Two experiments 
were accordingly made with this host. 
Experiment 1.—^Seven temperatures were employed , t as indicated* In 
TaJbJe VI., The soil used had 'bee 4 "steam : sterflized‘ afifr then liidculated * 
with; Corticium vqgum 9 four wee^s prior to the planting of tlie* beans', 
and had groyrn during this peqocjltwodrops'of cress and radish fedtidlihg^. 
Before the beans, wjere planted, however, the inoculated soil iri the variotri 
cans v \yas emptied and thoroughly mixed. Three caffs’ w£i*£‘ thferi 'filled 1 
with the_ inoculated soil at each tdnperature, and'fiheeti 1 'seeds' 10 plhfit&d 
8 These temperatures were the highest which were maintained in the experiments and possibly do'not 
india*t£ tbe pptiijium for£$rly gtowjtb.< ; M , , 
• The fungus used in these experiments was the same as that employed in Experiments i aha 2 on the pda:. 
10 The bean seed was .grown at the Utah Agricultural E^peritnent Station and exhibited np signg of 
disease. Precautions were taken before planting to free the seed of all adhering organisms by treating 1 
for 10 minutes in mercuric chlorid solution (i - -1,000). 
