The categories of plant products which directly affect human life: submitted for the Anderson-Henry Prize in Botany, 1936It has been impossible in the short space of
an essay to mention all the plant products which
directly affect human life, but, without any claim
to completeness, it may be said that almost every
species of really first -rate importance has been
mentioned. When it is remembered that there are
something like 250,000 known species of flowering
plants, it is realised that man utilises intensively
a mere handful of the available flora.It would seem that man, early in his history,
exploited the cream of the world's useful plants, and
that they have sufficed him ever since. Civilisation
has tended to spread already utilised species rather
than develop new ones. This is not to say that no
others can be used, but that, as is natural enough,
the line of least resistance has been pursued. While
the products of one species suffice there is little
inducement to develop others, but if the source of
raw material is cut off, additional species formerly
ignored are soon pressed into use. This was
strikingly illustrated during the Great War. The
plants which can be thus utilised when need arises
constitute, as it were, a reserve for future
exploitation.While little has been done as yet by modern
science in the direction of developing entirely new
cultivated species from natural wild plants, much
has been done in the way of improving existing
varieties of valuable cultivated plants, and in increasing
crop yield by manuring and rotation.Until about half a century ago, the only methods
known of improving plant breeds were selection and
hybridisation, but a far more valuable method is now
available, thanks to the researches of Mendel. It
is impossible to discuss the vast subject of Mendelism
here, but expressed shortly its value lies in that,
by following certain well defined laws, it is possible
to vary the constitution of a race very much, and to
eliminate many undesirable characters.In the control and prevention of plant diseases
scientific investigation again has been of the
greatest possible value. Some diseases have been
eradicated almost completely, and others brought
under some degree of control.The trend of modern agriculture then appears
to be in the direction of the improvement of existing
species of cultivated plants, and in increasing the
yield per acre of cultivated land.Finally might I emphasise just once again the
dependence of man on the plant world. The most fundamental fact about the human race is that, biologically,
man is an animal, and is in the most
fundamental respects little different from the
other members of that class. It is true that man
has, by the development of reason, risen to a
position of dominance over other living things, but
the high level of culture which he has attained has
increased rather than lowered his dependence on
plant products. He is indeed a parasite on the
green leaf
