PDF - CES (IISc)

xxvi
INTRODUCTION
the cortex have been induced by the action of the alga on the fungus.
The larger part of the thallus might therefore be regarded as equivalent to
a gall: "it is a cecidium, an algal cecidium, a generalized biomorphogenesis."
The morphological characters of lichens are of exceptional interest, conditioned
as they are by the interaction of the two symbionts, and new
structures have been evolved by the fungus which provides the general
tissue system. Lichens are plants of physiological symbiotic origin, and that
aspect of their life-history has been steadily kept in view in this work. There
are many new requirements which have had to be met by the lichen hyphae,
and the differences between them and the true fungal hyphae have been
considered, as these are manifested in the internal economy of the com-
pound plant, and in its reaction to external influences such as light, heat,
moisture, etc.
The pioneers of botanical science were of necessity occupied almost
exclusively with collecting and describing plants. As the number of known
lichens gradually accumulated, affinities were recognized and more or less
successful efforts were made to tabulate them in classes, orders, etc. It was
a marvellous power of observation that enabled the early workers to arrange
the first schemes of classification. Increasing knowledge aided by improved
microscopes has necessitated changes, but the old fundamental "genus"
Lichen is practically equivalent to the Class Lichenes.
The study of lichens has been a slow and gradual process, with a con-
tinual conflict of opinion as to the meaning of these puzzling plants their
structure, reproduction, manner of subsistence and classification as well as
their relation to other plants.. It has been found desirable to treat these
different subjects from a historical aspect, as only thus can a true under-
standing be gained, or a true judgment formed as to the present condition
of the science. It is the story of the evolution of lichenology as well as of
lichens that has yielded so much of interest and importance.
The lichenologist may claim several advantages in. the study of his
subject : the abundant material almost everywhere to hand in country
districts, the ease with which the plants are preserved, and, not least, the
interest excited by the changes and variations induced by growth conditions ;
there are a whole series of problems and puzzles barely touched on as yet
that are waiting to be solved.
In field work, it is important to note accurately and carefully the nature
of the substratum as well as the locality. Crustaceous species should be
gathered if possible along with part of the wood or rock to which they are
attached ;
if they are scraped off, the pieces may be reassembled on gummed
paper, but that is less satisfactory. The larger forms are more easily secured;