572 Ridley.— On Endemism and the Mutation Theory . 
for life of an individual or species, it is the struggle for successful continuous 
propagation. In most cases thousands of the seeds produced are absolutely- 
wasted, only those are not which find a suitable spot for their future repro- 
duction. A species modified for life in the full sun of a heath may, increas- 
ing the width of its leaves, first push into the thin scrub of the forest edge, 
and, gradually modified, may eventually become adapted for life in the 
dark, wet forest ; or it may modify itself to grow in salt mud, swamp, 
the sand of the shore, or on coral rocks or on mountain tops. 
Very Common Plants, 
On p. 17 of Ann. Bot., vol. xxx, Dr. Willis in dealing with very common 
plants writes : £ Why should a species that ranges over Ceylon and Peninsular 
India be commoner in Ceylon than one that only ranges over Ceylon ? 5 and 
makes the advocates (of Natural Selection I suppose) reply: ‘Because 
it has a wider range.’ This, he says, is simply an appeal to ignorance ; and 
here I heartily agree with him, merely suggesting he should refer the ques- 
tion to an observer of plants in place of such advocates. His suggestion is, 
that the reason why mere wide range should involve commonness is their 
greater age within the country. 
Let us examine the story of some common plants, and first take 
Imperata cylindrical the Grass known as Lalang in Malay and as Illuk 
in Ceylon. It was, when I first reached the Malay Peninsula, the com- 
monest plant in the peninsula. There was over large areas much more 
of it in bulk than any other plant, and far more than of any indigenous 
Grass in the whole peninsula. 
It is generally believed to be a native of Africa, and was probably 
introduced somewhere about 1822 into the Straits, when the forests of the 
country were cleared. According to Dr. Willis’s theory it must have been 
a much older inhabitant than, say, the indigenous endemic Saccharum 
Ridleyi , confined to the sandy heaths of Pahang. But we know that it is 
quite a modern introduction. Why should it be so much more abundant ? 
The plant has an underground rhizome which can grow at a depth of 
1 6 inches below ground, and if dug up can propagate itself rapidly from 
portions of the rhizome. Excessive heat and drought do not affect it, 
as the rhizome is too deep in the ground to be injured. Fire passing over 
the ground merely burns the leaves, which spring up again, growing an inch 
a day. The plumed seed is readily carried along into distant spots. I have 
even seen it growing in the sulphurous smoke of a volcano in Java, where 
hardly another plant could hold its own. We have another species in the 
country — /, exaltata , Brongn. This appears to have originated in South 
America, and occurs too in the New Hebrides and Malay islands, and the 
Malay Peninsula as far north as Mergui. It is closely allied, a rather taller 
