istic growth.

There is, as yet, no conclusive evidence on many of the matters concerning
the relation of vitamines to plant growth. But it seems that these
substances are of almost universal occurrence in the organic world; that
they are not of the same general type as other substances which are
essential to the nutrition of plants or animals, but have specific
stimulating or regulating effects upon the physiological activities of the
organism; that the vitamines which are essential to animal life are
elaborated by plant tissues, but that in the case of the bacilli of certain
human diseases there seems to be some indication that the affected tissues
of the animal host produce vitamines which are essential, or favorable, to
the growth of the parasitic organism. There seems, therefore, to be
evidence of a mutual relation between plants and animals with respect to
their nutritional needs for the so-called "vitamines." But the evidence
concerning the function of these substances in the tissues of the organism
which elaborates them is, as yet, inadequate to provide any clear
conception of the reason for their development or of the mechanism by which
they are elaborated. Neither is there, as yet, any conclusive evidence
concerning the chemical nature of the substances themselves.

AUXIMONES

Certain investigations have indicated that bacteria, at least, develop
exogenous vitamines which are beneficial to the growth of other plants.
These are the so-called "auximones." For example, bacterized peat seems to
contain auximones which may be isolated from the peat and exert a
beneficial effect upon the growth of various seed-plants, including common
farm crops. Neither the original experimental data, nor the theories which
have been advanced to account for the observed beneficial effects of the
supposed "auximones" have, as yet, sufficient confirmatory evidence
definitely to establish their soundness. But it seems that there is a
probability that some plants, at least, do elaborate vitamines, or
auximones, which are useful to other plants.

TOXINS

Toxins are substances which affect injuriously the normal activities of the
organism. As has been pointed out, they may be the same substances which,
in lesser concentrations, exert a stimulating effect upon the same
organism. Hence, it is probably inaccurate to discuss the toxins as a
distinct group of substance