46 Transactions British Mycological Soctety. 
in every few years.’’ In order to retain the number of individuals 
of a species stationary it is only necessary that one mature plant 
should be produced during the period of growth of the parent— 
if more occur the species will tend to oust out all other species. 
“ Linnaeus has calculated that if an annual plant produced only 
two seeds—and there is no plant so unproductive as this—and 
their seedlings next year produced two, and so on, then in 
twenty years there would be a million plants....It would suffice 
to keep up the full number of a tree, which lived on an average 
for a thousand years, if a single seed were produced once in a 
thousand years, supposing that this seed were never destroyed, 
and could be ensured to germinate in a fitting place*.”’ To give 
an idea of what the above figures for Orchis maculata really 
mean Darwin worked out the possible rate of increase. “‘An 
acre of land would hold 174,240 plants, each having a space of 
six inches square, and this would be just sufficient for their 
growth; so that, making the fair allowance of 400 bad seeds in 
each capsule, an acre would be thickly clothed by the progeny 
of a single plant. At the same rate of increase, the grandchildren 
would cover a space slightly exceeding the Isle of Anglesea; and 
the great grandchildren of a single plant would nearly (in the 
rate of 47 to 50) clothe with a uniform green carpet the entire 
surface of the land throughout the globe’”—and as O. maculata 
is perennial, the parent plant would still be alive! 
But even these numbers in our native orchids are much ex- 
ceeded by those of tropical species. Scott estimated that a 
capsule of Acropera contains 371,250 seeds and, judging from 
the number of flowers borne by the plant, the total number of 
seeds for an individual would be 74,000,000: Charlesworth esti- 
mated 825,000 seeds for a single capsule of Cymbidium Tracey- 
anum: Muller 1,756,440 seeds for a single capsule of Maxillania. 
It appears to be a general biological rule that where the con- 
ditions of successful germination are difficult of attainment a 
prolific number of seeds (or spores) are produced and, vice versa, 
where the requirements are not of a specialized nature, a smaller 
number occur. 
In the case of orchids it seems not unlikely that the enormous 
seed production is in some way related to the fungus question. 
Their small size, their lightness, their net-work integument and 
the presence in some genera of elaters ensure. their effective 
dissemination. But unless the necessary fungus be to hand no 
germination occurs—the seed may develop to a certain extent, 
but it does not produce roots unless the appropriate fungus 
enters its cells. 
So far, however, we know nothing of the distribution of these 
* C, Darwin, Origin of Species (1859). 
