Native Hawaiian Cotton — Stephens 
391 
orous stands of tomentosum were found under 
light shade. 
The virtual restriction of tomentosum to old 
volcanic outcrops, as opposed to friable soil, 
suggests that it possibly may have rather special- 
ized physical and nutritional requirements. Mac- 
Caughey (loc. cit.) included it in a list of 
species which he considered to be particularly 
adapted to the colonization of lava flows and 
which were characterized by certain xerophytic 
features. Some of these features are clearly ap- 
plicable to tomentosum ( viz woody perennial 
growth form, with slow growth and deep root 
penetration; foliage often pubescent; and a 
tendency to assume a decumbent habit on bare 
substrates). He also pointed out the extremely 
xerophytic conditions which are generated on 
recent lava flows through a combination of 
high evaporation, free drainage, and rapid heat- 
ing of black or almost black surfaces. However, 
these conditions apply particularly to recent lava 
flows, and in the present study no tomentosum 
was found in those areas (Hawaii and East 
Maui) to which recent flows are restricted. 
It seems likely that some of the difficulties 
of growing the species in culture may be as- 
sociated with (a) failure to provide sufficiently 
rapid drainage, (b) too high a mean tempera- 
ture, and (c) too acid soil conditions. With 
regard to the third factor, MacCaughey (1917: 
408) noted that soils derived from Hawaiian 
lava flows have a far higher proportion of basic 
constituents than comparable mainland soils 
(64% as compared with 19%, according to his 
figures ) . The following analysis of igneous rocks 
in Hawaii was obtained from "Handbook of 
Hawaiian Soils” ( 1935 ) : 
Average of 56 Analyses of Lavas from 
Island of Hawaii 
Si0 2 
50 
Na 2 C >3 
3 
A 1203 
14 
k 2 o 
1 
Ee 2 03 
3 
Ti 2 Oo 
3 
FeO 
9 
P205 
0.5 
MgO 
8 
MnO 
0.1 
CaO 
9 
MORPHOLOGICAL VARIATION 
Those morphological characteristics of to- 
mentosum which distinguish it taxonomically 
from the other New World species of Gossyp- 
ium ( long anther filaments, partly fused in 
pairs; absence of leaf nectary; intense yellow 
flower color; undifferentiated and strongly ad- 
herent seed fibers) were found to be quite 
uniform. On the other hand, characters which 
previous experience had shown to be rather 
variable (leaf shape; bracteole form and dis- 
section; degree of pubescence; plant habit) 
were found to be extremely variable. There was 
little if any tendency for these variations to 
follow a geographical pattern; i.e., it was not 
possible to distinguish morphologically between 
different island races. In this respect, G. tomen- 
tosum contrasts strongly with the native species 
of the Galapagos Islands (G. darwinii ), in which 
each island has tended to develop its own well- 
marked morphological race. It is somewhat 
surprising that two archipelagos, of comparable 
size and origin, and offering similar arid habitats 
to related colonizing species, should have pro- 
duced such different evolutionary results. 
The nature of variation in leaf shape and 
bracteole form is illustrated in Table 1 and Fig- 
ure 3, respectively. The data show the consider- 
able range of variation within any one popu- 
lation, and the extensive overlap that exists 
when different populations are compared. Varia- 
* i * a§4 
i t Alii 
tIAAAi 
tit it 
Fig. 3. Outline drawings, approximate half natural 
size, of tomentosum bracteoles. All bracteoles were 
obtained from open flowers. Top row, Oahu; 2nd row, 
Lanai; 3rd row, Molokai; 4th row, Maui. 
