16 TOXIC SUBSTANCE EXCRETED BY PLANTS. 
While this note has been going through the press I have 
received Bulletin No. 40 of the Bureau of Soils, (United 
States of America) by Messrs. Schreiner and Reed on “ Some 
factors influencing soil fertility.” In this Bulletin the authors 
come to the conclusion that ‘ the excreta of the cow pea roots are 
very slightly toxic to roots of wheat seedlings” (page 35), and 
that “the excreta of oats are more toxic to the roots of wheat 
seedlings than those of corn or cow peas—a conclusion that is 
substantiated by the results obtained in crop rotations” (page 36). 
The experimental data given in the Bulletin do not justity 
these conclusions but only indicate that the excreta from cow 
peas when in the urlitriry concentration obtaining im their eaperr- 
ments are very slightly toxic to roots of wheat seedlings when 
these lutter are at the stuge of growth of those used in the experiment. 
I find that very young plants are not affected, by a toxic 
solution of given strength so rapidly as older plants. doubtless 
because the latter. owing to more rapid transpiration, take in the 
toxic substance in larger quantities. 
Again, the impossibility of the statement made with regard 
to the excreta of oats being more toxic than that of cow peas or 
corn is self-evident, implying as it does that any quantity however 
yreat trom oats is more toxic than any quantity however small 
from cow peas or corn. 
The media that were compared contained quite arbitrary 
amounts of excreta from an arbitrary number of plants growing 
for an arbitrary period, it being stated that “the agar containing 
their exeretions was obtained in each case by planting a large 
number of seedlings ina dish of soft agar and allowing them to 
grow for eight to fifteen days according to the kind of plant 
employed.” 
There are no data in the Bulletin under reference which 
indicate that the excreta from all the plants tried are not identical 
in character. 
