APRIL 15, 1915] 
NATURE 
187 

diminishes, while the subject thinks he is writing 
faster. 
The pressure curves obtained from children differ 
from all the adult types. A flat-topped curve had 
been considered until recently the characteristic child’s 
curve (Fig. 3, Il.a). This curve does not, however, 
represent the first stage in the acquiring of writing. 
The first curves obtained are more or less character- 
istically drawing curves (Fig. 3, I.). Such curves are 
best seen where the child begins with printed letters 
rather than script (Fig. 3, I.c). In this case each 
stroke requires a definite and separate impulse, and 
this is well marked in the pressure curve. In the 
earliest script the curve seems merely irregular, but 
this is due to variations in the drawing unit with 
which the child is dealing, which may be a single 
stroke, a letter, or a group of letters. The second 
stage in learning to write is marked by what was 
formerly called the child type of pressure curve, a 
curve with a strikingly regular, flat top, which is 
still a drawing curve, though the child is now draw- 
ing the whole word. This curve passes gradually 
into the curve with rippled top of adult writing, the 
time when the transition can really be said to take 
place being about the age of ten or eleven (Fig. 3, 
III.). The transition seems to mean two things. In 
the first place the necessary co-ordinations are estab- 
lished to such an extent that the mechanism of writ- 
ing works without attention to the individual strokes 
and forms which the hand is making. In the second 
place, and partly because of this, writing has ceased 
to be drawing and has become language, the rhythm- 
ical variations in point pressure corresponding to | 
the rhythmical variations in grip pressure, and being 
analogous to a certain extent to the rhythm of speech. 
When this stage is reached the impulse under the 
direction of which writing takes place is distinctly a 
word impulse, and sometimes even a phrase or sen- 
tence impulse. 
fails to show this characteristic rhythm of adult writ- 
ing, while drugs like alcohol tend to impair the 
rhythm and ultimately to break it down altogether, 
apparently because of their effect on co-ordination. 
It is also somewhat interesting to find that the pres- 
sure curve is almost as characteristic of an individual 
as his signature, and persists even in left-hand writing 
without previous practice. There is evidently a wide 
field for investigation in this direction, and perhaps 
we may yet see the development of a real science of 
graphology based upon such investigation. 

FLORA OF ADEN.} 
psoe BLATTER has brought together an inter- 
esting account of the vegetation of the Aden 
peninsula, in which, after summarising the history of 
botanical exploration of this region from the earliest 
times, he gives data regarding physiography, climate, 
soils, tabulated lists of the plants, and brief notes on 
their distribution, origin, means of dispersal, etc. No 
references are made to work on plant ecology, but a 
comparison of the characters of the Aden vegetation 
with that of other arid regions, as investigated par- 
ticularly by the Carnegie Institution botanical staff 
in North American and North African deserts, brings 
out some points of considerable ecological interest. 
The first botanical description of Aden was given 
by Ibn Batuta in about 1330, and it consisted of the 
brief statement that ‘there are neither seeds nor trees 
1 “*The Flora of Aden.” By Ethelbert Blatter, Professor of Botany at 
St. Xavier's College, Bombay. Records of the Botanical Survey of India. 
Vol. vii, No. 1, Calcutta, 1914. Pp. iit+79; 5 plates; 1 map. 
NO. 2372, VOL. 95| 

nor water.’’ Though Aden is not so entirely destitute 
of vegetation as this famous traveller supposed, the 
impression it produced upon much more recent botani- 
cal visitors was scarcely more favourable. Sir J. D. 
Hooker, in 1847, described Aden as being ‘upon the 
whole the ugliest, blackest, most desolate, and most 
dislocated piece of land, of its size, that ever I set 
eyes upon, and I have seen a good many ugly places”’; 
but he mentioned the comparatively fertile lower 
valleys, thickly studded with beautiful-flowered shrubs 
and small trees. Prof. Blatter’s compilation is based 
largely upon the scattered reports and collections 
made by residents and visitors, and shows that Aden, 
despite the fact that it consists largely of “bare naked 
rocks which cannot find their equal in any part of the 
world as regards dryness, infernal heat, and barren- 
ness,”’ possesses an interesting and surprisingly varied 
vegetation. 
The volcanic rocks forming the greater part of the 
Aden peninsula, which is about fifteen miles in circum- 
ference, are practically devoid of plant life; even 
lichens are scarce on the sun-baked and disintegrating 
rock-surfaces. These lofty and jagged rocks, rising in 
places to 1700 ft. altitude, are scored by steep gulleys 
and mostly run straight down to the shore, but here 
| and there the lower slopes are gentle or almost flat, 
and in such places the clayey soil retains rain-wash, 
which elsewhere quickly runs off or percolates through 
the loose soil, and the vegetation in these parts is 
fairly rich. Apart from such habitats, the rigorous 
character of the conditions with which the Aden 
plants have to contend may be realised from the facts 
that there are no permanent streams or springs or 
marshes or ponds; the annual rainfall rarely exceeds 
| six or seven inches in the wettest years; no rain may 
fall for two years at a time, and when it does fall 
it usually comes down in a torrent lasting for a day 
or two, changing the dry gulleys into turbulent 
| streams which quickly dry up again. 
It has also been found that the writing of defectives | 
The Aden flora consists of 250 species of flowering 
plants, including ten trees, fifty-eight shrubs, forty-six 
undershrubs, and 136 herbs. The work of the 
Carnegie Institution botanists has shown that in the 
most arid regions of the earth, where the rainfall is 
extremely scanty, infrequent and irregular, what were 
formerly regarded as the typical desert-plants, namely, 
species with fleshy water-storing leaves and stems 
(cacti, etc.), are almost or entirely absent, and that 
the desert type par excellence is not succulent, but 
sclerophyllous. This term is applied to plants which 
do not store up water but contend with the extreme 
aridity of their environment by various adaptations 
for reducing water-loss to a minimum—reduced leaf 
surface, dense hair-covering, waxy cuticle, gummy 
epidermis, development of leaves or branches or both 
as spines, etc. From Prof. Blatter’s list such plants 
appear to be dominant in the vegetation of Aden; 
fleshy species are practically confined to the sea- 
coast. A further point of interest is that about half 
of the herbaceous plants listed for Aden are short- 
lived annuals, which grow in the clayey soil of the 
flats and gentle slopes where water can be retained 
in the surface layers long enough for these plants to 
complete their brief life-cycle whenever rain comes. 
This, again, is a characteristic feature of the typical 
desert flora with clayey oases. 
The records of the Botanical Survey of India con- 
tain so much that is, at any rate potentially, of general 
interest to students of plant ecology, that while the 
material they contain is welcome and useful, it is 
much to be hoped that the survey workers will make 
themselves acquainted with what has been and is being 
done on modern ecological lines, so that they may 
