VALUE OF CHARACTERS. 373 
Andryala from Crepis, of Bedfordia from Senecio, &c.; a certain 
glandular odoriferous indumentum is characteristic of most 
Madiee, Buphthalmes, and a few others; and many other in- 
stances of the generic value of differences in the nature of hairs 
might be adduced, although the subject has not as yet been suffi- 
ciently worked out. The presence or absence, abundance or 
paucity, greater or less development of any description of indu- 
mentum appears never to be of more than specific value. 
ll. Differences in Geographical Distribution. 
I purpose entering into the geographical distribution of Com- 
posite under a separate head. I only mention it now to show the 
importance of taking it into consideration in the demarcation of 
generic groups. If the two theories be admitted, that allied 
species and genera have a common origin, and that the descen- 
dants of a common stock placed in different regions having no in- 
tercommunication will vary in these different regions with different 
combinations of characters, it will be seen how much geographical 
distribution may be made to check the value given to generic or 
other groups founded upon technical distinctions. But the use of 
geographical distribution as a generic character is liable to many 
errors. There are especially two great difficulties to overcome :— 
first to determine upon how far geographical distribution is due to 
origin, and how far to climatological influences; and, secondly, to 
decide upon the all-important distinctions between what we may, 
with Hewett Watson, designate as true denizens of a country, 
colonists, and aliens: and even among the denizens a still more 
difficult, although important, point for consideration is the remote- 
ness of the period at which the common stock has been connected 
with the flora of other countries. For instance, the Helichrysee, 
as well as the Arctotidew (Cymbonotus), of Australia are ciosely 
allied to the corresponding South-African groups without having 
a single species in common, excepting such as are known to be 
modern colonists. In the case of Helichrysee the forms have 
multiplied exceedingly in both regions in the same or in different 
directions, and have every right to be designated as true native 
races. But Arctotideæ, numerous in South Africa, have assumed 
only one form in Australia. Is that form to be regarded as 
of contemporaneous origin with others common to the two regions, 
but modified into a local generic type, or is it some old colonist 
still to be found, or perhaps now extinct, in South Africa? isa 
question which remains undecided. 
