Man's Footsteps. 21 
obvious, but having been grown from joints for ages, it 
has lost its power of seed bearing, and therefore is 
unable to exist apart from cultivation. The banana is 
another instance of loss of power through disuse ; when 
left to itself it sometimes produces a few black specks 
inside the fruit, but never perfect seeds. Other familiar 
examples of the development of one faculty at the 
expense of another, will be found among the sweet 
herbs, such as mint and thyme, which rarely flower 
under cultivation. The toya (Dianthera pectoralis) 
although so commonly grown in Georgetown is never 
seen in flower, while on the contrary in the wild state it 
flowers freely. 
A very large proportion of the commonest weeds are 
of annual duration. In developing plants of this class 
in temperate climates, the change of seasons must have 
been the principal factor. Where however plants are 
not subject to alternations of cold and heat, drought and 
deluge, annual plants are entirely absent. In the forests 
of Guiana all the species are perennial, while on the 
savannahs where the seasons have more influence annual 
plants are not uncommon. A rather interesting example 
of the apparent development of an annual plant from 
a perennial may be seen in the common silver fern 
(Gymnogramma calomelanos) . This plant may be 
considered as one of " Man's Footsteps " as it is always 
found in clearings, on old brick-work, or on the sides of 
estates' trenches, appearing as if the spores were 
brought to light by turning up the soil. Like nearly all 
ferns it is perennial, but a rather curious circumstance in 
connection with its manner of growth in British Guiana 
is the fact that it behaves as an annual under certain 
