COLONIZING SPECIES, 575 
at the time of their arrival, or if their germination is slow when 
the conditions are such as to produce it, the chances are that the 
seeds will have died or have been destroyed before they have 
fixed themselves in the soil The rapid germination of small 
Seeds is probably an essential condition of the above-mentioned 
sudden appearance of large numbers of Blumeas and others, and 
enables certain plants, which chance has thus brought, immediately 
to take almost exclusive possession of cleared grounds, fresh 
turned-up soil, drained lakes, &c., as in the case of the Senecio 
that covered the bed of the lake of Haarlem the first year after 
the water was drained off. Marsh and aquatic plants, when of 
ready germination, enjoy peculiar facilities for establishing them- 
selves; for, as a rule, they find the physical conditions almost at 
all times and seasons equally favourable for their germination. 
These plants are rare in Composite ; and a considerable proportion 
of those that are known (Sparganophorus, Enhydra, Aster acris, 
A. salignus, &c.) are amongst the widely dispersed or amphigeous 
plants or distant colonists. Ready germination is probably also an 
essential element in the spread of annual escapes from cultivation. 
Where seeds are few or of slow germination, great vitality and 
external protection are most useful; and these, more even than the 
burr-like facilities for transport, have probably effected the noxious 
multiplication of the Xanthiums. Securely encased in a bony 
envelope, which may defy the efforts of most of its enemies to 
reach the scanty food within, the seed may await the occurrence 
of favourable conditions for germination, through successive 
seasons which would utterly destroy myriads of the smaller 
unprotected seeds. Similar causes may perhaps similarly facilitate 
the establishment of some of the Centaureas, which have usually 
but few good achenes enclosed in their hard prickly involucres. 
But successful germination, however abundant, is not sufficient 
to establish a colonist if it has not among its inherent properties 
those which will enable it to hold its own against the numerous 
enemies which will attack it, the numerous rivals which will 
dispute the possession of the soil. Enormous reproduction is 
insufficient without individual tenacity of life. The Senecios, 
Blumeas, Erigerons, Conyzas, which may cover new ground and 
produce their seed a thousandfold, ten thousandfold, or more, 
may succumb in the course of a few years to the individually 
vigorous denizens that may gain a footing amongst them, in the 
Same manner as we see vigorous foreigners (like Cryptostemma in 
LINN. JOURN.—BOTANY, VOL. XIII. 28 
