RELATION OF SOME RUSTS TO THEIR HOSTS 
207 
Table VII 
The Effect of Nutritive Solutions Upon Spore Germination and Continuance of Growth 
of Puccinia Sorghi 
Solution 
Germination 
Length of Germ-tube 
Remarks 
Conductivity water 
good 
400-500 micr. 
unbranched 
Mineral nutrient 
slight 
160 
Cane sugar 5% 
fair 
160-800 " 
Cane sugar i % 
good 
400-800 " 
Cane sugar 5% + nut 
none 
Maltose 5% 
fair 
about 100 " 
Maltose i % 
good 
300-800 " 
branched some 
Maltose 5% + nut 
very slight 
about 100 " 
unbranched 
Peptone 1% 
fair 
" 500 " 
branched much 
Peptone i % + nut 
none 
Duggar's nut + .5% peptone. . . . 
none 
Asparagine saturated 
slight 
160 " 
branched 
Asparagine 1%..., 
fair 
80-100 " 
Leucine i % 
slight 
100-400 " 
" slightly 
they shortened the length of the germ-tube, an experiment was under- 
taken to study the germination and development of the rust at low 
concentrations. Two solutions, i percent cane sugar and i percent 
cane sugar plus mineral nutrient (see Experiment 41) were used as the 
basis of this series. Dilutions of 1/2, 1/8, 1/32, 1/128, 1/512, and 
1/1024 of this strength were made. Hanging drops of uredospores 
of Puccinia Sorghi were made in these solutions as in the preceding 
experiment. 
No difference was noticed in the amount of germination in these 
solutions. The length of the germ tube was the greatest (400-800 
micr.) in 1/8, 1/2 and I percent cane sugar. In the other solutions, 
the length varied between 160-400 micr. The rust died in all solutions 
in about three days. 
Experiment 43. — In this experiment, plant extracts were used. 
A decoction of leaves of corn was made by autoclaving pieces of corn 
plants (i part by vol. to 5 parts of distilled water) at 10 pounds pres- 
sure for 30 minutes. An uncooked extract of the plant was made by 
cutting up sterile plants as finely as possible and adding sterile distilled 
water to them and then letting the mixture stand for 24 hours. A 
third extract was made from sterile germinated seeds which were cut 
up in sterile distilled water. Two or three seeds were used for 25 cc. 
of water. Uredospores of Puccinia Sorghi from pure cultures of the 
rust were sown in hanging drops and in capsules of the solutions. 
The germination in all cases was good. In the decoction of the 
