IOWA ACADEMY OP SCIENCE 
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the plant which it is decided to use are germinated, and when the radicles are 
a few mm. long they are placed in the solution to he tested, and the effect of 
the solution on the growth and vitality of the radicles is noted. It is not a 
question of nutrition and no plant food problem can he attacked in this way. 
The radicle is fed hy the store of plant food in the seed, and any effect which 
a solution may have is due to injury or, it may he, stimulation. The radicles 
are extremely sensitive and this makes it a very delicate test. The ordinary 
distilled water of our laboratories is entirely unfit for use in these investiga- 
tions and especial precautions are always taken to get non-toxic water. This 
shows the delicacy of the method. 
The presence of a toxin in the burs was tested by this method which may 
be called the Plant Radicle Method. Corn was first used as an indicator. 15 g. 
of dry burs were ground as fine as possible, placed in a small cloth sack, 
boiled in distilled water, and the extract thus obtained brought to 100 c. c. 
This extract contained 1.35 per cent solid matter and is designated in the 
following tables as ext. N. Diluted to twice this volume it is called N — 2, 
etc. No mold would grow on this extract, either N strength or N — 2 strength, 
even when inoculated with mold. This shows that it was toxic to mold. 
The corn seedlings used were germinated between sheets of filter paper and 
the moisture supplied by wet sphagnum moss above and below these sheets. 
Fresh sheets were used each time to avoid mold. Seedlings that developed 
normally and with straight radicles were used. The test was made in test 
tubes of various sizes, all the tubes of one series, however, being of a size. 
A cork was made to fit the tube, the radicle of the seedling was passed through 
a hole in the cork and into the liquid to be tested, which filled the tube up to 
the cork. The length of the radicle was marked on the outside of the tube 
by a blue pencil. The seedlings were allowed to remain in this position for 
twenty-four hours and the growth if any v-as measured by holding the tube 
up before the eye and measuring from the blue mark to the end of the radicle. 
This could be very easily and accurately done. The solution was then emptied, 
the tube cleaned carefully, filled with distilled water, the seedling rinsed and 
replaced, and the position of the end of the radicle marked on the glass. In 
twenty-four hours the growth was again noted. This second day’s growth in 
distilled water was to determine the condition of the radicle. If no elonga- 
tion took place it was dead. If it was as long as the check it was uninjured. 
If the elongation was less than the check it was injured, and the degree of 
injury could be very accurately judged by noting the amount of retardation. 
Observations confined to the first day are not conclusive. The best and most 
practical test for vitality is the ability to grow when taken out of the toxic 
solution and placed in distilled water. The above method is a slight modifica- 
tion of that used by Loew and Dandeno, which seems to be the best and most 
convenient of all the methods given.^ 
