204 SOME MINOR PROBLEMS CONCERNING, ETC.
in the earth. That the dissemination of the seeds of plants being
entrusted to wind, water, animal, or other agencies, introduces an
element which it is not possible to calculate. That, although the
possibilities of these agencies are very great, they may not be in con-
tinual operation, as there is evidence to show that in some cases
plants spread very slowly. That some apparent anomalies in dis-
tribution may arise from those plants which are incapable of pro-
pagating themselves by seed.
That the nidus on which a seed falls also affects distribution, and
that certain peculiar floras are due to this cause, although Essex may
not be looked upon as a typical county in that respect. That the
difficulties of plant colonization in Essex as shown by present diffi-
culties with raw boulder clay must in earlier times have been very
great.
Then has been noted the similarity and dissimilarity of our Essex
wild vegetation compared with certain tracts north and south of the
county.
Lastly, that the hand of man has been instrumental in extinguish-
ing certain forms in this locality, and has perhaps been instrumental
in saving a few others, but that on the whole there is a diminution of
native forms. That man has also circumscribed the area and so
brought into more prominent play the factor known as the struggle
for life. That the ultimate outcome of this struggle for life, although
sometimes checked by the farmer in clearing away rank vegetation,
must deprive us of many fragile forms which still survive as rare
plants. That our historical knowledge of common species is often
very imperfect, and that observations of them should be put upon
record in order to detect incipient changes in distribution.
Recorded observations are infinitesimal contributions to the sum
of human knowledge, yet this sum of knowledge goes but a little way
in unravelling problems in which life is concerned. Take these
problems of distribution for instance. They have their root in geo-
logical time, where the evidence is for the most part swept away.
Moreover, if we could question every species as to its history, we
could not question every individual as to its environment, both of
which are indispensable considerations in any acceptable solution
of these problems.