Page:The Journal of Indian Botany, Volume III.djvu/62

32 succession as understood in Oecology. Probably this will be universally admitted and it will not be necessary to discuss the point further.

From what has been said it follows that the small area in question may not be at any time (and probably in fact is not) a pure formation, i.e., pure meadow, or pure marsh, or pure xerophytic bushland. The latter will be most nearly pure of the three, say in May, but the ground will still contain the resting organs (rhizomes, etc.) of the plants of the other two formations and possibly a very few hardy and persistent survivals of the marsh. So that in fact our area bears a mixture of three (or two if marsh does not develop) formations, the relative importance of which varies with the progression of time. This is the idea which forms the title of this essay "Mixed formations in time." It is necessary to distinguish the case quite clearly from the already familiar one of a mixed formation between two pure ones, in a relatively narrow zone where they overlap. For instance woodland instead of passing over abruptly into pure grassland may first pass into an intermediate mixed zone of grassland with scattered trees. This is quite distinctly a case of mixed formations in space. Time does not effect the relationship in any regularly recurrent manner.

The diagram appended is meant to be no more than hypothetical, but it may serve to visualize the idea of mixed formations in time. The plain dotted line represents the relative dominance of the xerophytic formation, the—•—•—line shows the same for the mesophytic and the—•••—•••—line the relative dominance of helophytic vegetation. One point in the diagram may require emphasis, the vertical ordinate at any point is not meant to represent absolute dimensions, but only relative dominance.

DIAGRAM TO ILLUSTRATE MIXED FORMATIONS IN TIME.

Apart from the general argument I have followed, there appear to be definite facts, derived from a study of the physiological anatomy of plants of such a mixed formation, which lend support to the theory. It is not my purpose to state or discuss them at present, especially as they are very incompletely worked out.