ON GENERA AND SPECIES. 3 
but the different views entertained by botanists, respecting 
the data on which genera and species are founded, renders 
the study of Ferns a task of no ordinary labour. This is 
owing to many causes, one of which is found in the fact 
that many species are normally heteromorphous ; separate 
plants of the same species presenting different forms at 
the same or at different periods of growth, although grow- 
ing under the same climatic influences ; in some cases dif- 
ferent fronds of the same plant, and even portions of the 
same frond when seen apart, have been characterized as 
distinct species, and have even been placed under different 
genera. It also frequently happens that two or more speci- 
mens present sufficient characters to be considered distinct 
species, but when the intermediate gradations of the 
Series are supplied, only the most extreme states of any 
of the forms appear sufficiently distinct to.be so con- 
sidered. It often happens that plants of the same species 
_ atone time produce all simple, and at another time all 
pinnate or more highly divided fronds; it is therefore not 
surprising that different forms of individual species should 
. be viewed as representing two or more species when 
.. known only from incomplete herbarium specimens. 
It must also be borne in mind that the descriptions of 
. many species found in books are derived from dried speci- 
. mens, obtained in various parts of the world by trade 
: collectors whose object is often only pecuniary gain, and 
whose profits are dependent on the number of forms found. 
.. Great caution is therefore necessary in accepting a collector's d 
_ idea of species; it is only on the word of the independent H 
and truly scientific collector that we can rely for correct ` 
am information on the various aspects assumed by individual — 5 
| Midi whowiig Segen due sexy font whence wil. 
their history ; but even under the most favourable, eene 
