[Footnote 1: Kearney and Means, Agricultural explorations in Algeria,
Bul. No. 80, Bur. Plant Ind., U. S. Dept. Agric., 1905.]
[Footnote 2: A. Engler, Die Vegetation der Erde IX. Die Pflanzenwelt
Afrikas. 1 Bd., 1910, page 902.]
[Footnote 3: The seasonal distribution of rain (by percentages)
is somewhat different from that given by Engler, which is given in
the accompanying table.
+---------+-----------+-------+---------------+
| Season. | Littoral. | Tell. | High plateau. |
+---------+-----------+-------+---------------+
| Winter | 41 | 36 | 45 |
| Spring | 27 | 32 | 46 |
| Summer | 4 | 7 | 11 |
+---------+-----------+-------+---------------+
]
[Footnote 4: The most recent records available, 1897-1908, do not
give a satisfactory account of the precipitation on the desert. For
instance, meteorological records covering eight years for El Golea
do not report on the rainfall. Records of five years at In Salah
take the rainfall into account on one year only, and on that year
no precipitation occurred.]
[Footnote 5: Unless otherwise stated, the climatological statistics
given in this paper were taken or compiled from Observations
Météorologiques du Riseau Africain, 1907-1908. The evaporation
data are based on readings of the Piche evaporimeter. The amount of
evaporation given in the text can be reduced to the evaporation from
a free-water surface by multiplying by 0.737 (Meteorological Notes,
J. I. Craig. Cairo Scientific Journal, vol. vi, May 1912).]
[Footnote 6: At Touggourt, however, no rain was reported during
the summer season of 1908.]
[Footnote 7: Kearney and Means, _loc. cit._]
[Footnote 8: The Root Habits of Desert Plants. W. A. Cannon. Carnegie
Institution of Washington Publication No. 131. 1911. This paper gives
a descriptive classification of the main root-types in the deserts
of the southwest, in which such a root as found in _Acanthyllis_
is called _generalized_, in distinction to roots like those of
most of the cacti, or _Zizyphus_, the former having a system
wholly superficial and the latter a system wholly deeply placed,
as _specialized_. The specialized root-systems appear to be so fixed
in character as to be not easily changed, while the generalized type
is flexible. It will be self-evident that the type of root-systems
may be of great importance in determining the local distribution
of a species.]
[Footnote 9: Compare the root-system of _H. scoparium_ at Biskra,
p. 64.]
[Footnote 10: The most striking change in the general character of
the vegetation which the traveler notices as he goes from the less
arid to the more arid portion of southern Algeria is its decrease
in amount. This occurs through dwarfing effects of whatever cause
and through a decrease in the number of individuals. Within certain
limits the results observed are to be attributed mainly to the
first of these, since there is often a surprisingly large number of
perennials on any given area. But in other and more intensely arid
regions (as portions of the Arabian-Egyptian desert, and indeed
a limited area on the hamada between Ghardaia and Ouargla) plants
are wholly wanting. Whether such is generally the case on the reg
or the hamada farther south in southern Algeria is not known.]
[Footnote 11: Tristram remarks that it “seems that the larger wild
animals have been rapidly decreasing in numbers and are in process
of speedy extinction. Dr. Shaw, 150 years since, enumerates in his
travels . . . five species of ruminants, which from his descriptions
must be the bubale, the aoudad or wild sheep, the addax, and the
gazelle, as well as the stag. . . . As the population has not
increased, but rather retrograded, we can only surmise that the
substitution of the flint and steel gun for the matchlock of the
Bedouin . . . has been fatal in its results to all larger game.”
It may be remarked that the French impose such restrictions on
the Arab as regards the character of the guns he may use (only the
army and certain officials of the government employing modern arms)
that for the region visited Tristram’s description holds fairly
well for to-day.]
[Footnote 12: Statistique Générale de l’Algérie, 1908.]
[Footnote 13: Un voyage botanique au Sahara, Bull. Soc. Bot. Belg.,
1898.]
[Footnote 14: Massart, _loc. cit._]
[Footnote 15: Joan’s Guide de l’Algérie et de la Tunisie.]
[Footnote 16: Massart, _loc. cit._, p. 314, suggests that the Sahara
may be gradually becoming more arid and says that as a result the
betoum is becoming more and more rare and may become extinct. He says
“L’extinction du Pistacia atlantica présente le caractère, tout
à fait exceptionnel, d’ètre uniquement l’effet du climat.” It
will appear from what is said in this study regarding the effects of
grazing in general, as well as the especial effects on the betoum,
that if the betoum is becoming extinct the sole cause, or perhaps
the main cause, is not the adverse climate.]
[Footnote 17: Dr. Charles Amat, Le M’Zab et les M’Zabites,
p. 70, gives a somewhat higher temperature for the rocks of the
southern Chebka, placing it at 90° to 100° C., or even higher.]
[Footnote 18: Les Oasis du Souf et du M’Zab, La Géographie, 1902.]
[Footnote 19: Foureau, d’Alger au Congo par le Tchad, 1902,
mentions having met with indications of early settlement of the
Sahara by people now forgotten, and whose tombs, inscriptions, and
other remains, were well known by his Touareg servants, although
not at all understood by them. So far as I have learned, however,
it is not supposed that the region of the M’Zab was inhabited
before the coming of the Beni M’Zabs.]
[Footnote 20: There are seven cities of the Beni M’Zab, of which
five lie in the M’Zab Valley, close to one another. These are
El Ateuf, Ben Noura, Melika, Beni Isguen, and Ghardaia. In the
pre-French times these cities were bound together in a confederacy
with Ghardaia as the capital. The M’Zabites are at present,
and probably always have been, a peaceful trading folk. They are
heterodox Moslems. In an early time they aroused the antagonism of
their more warlike as well as more orthodox Arab neighbors of the
Tell, who drove them away from the coast region, and again from
Ouargla and other places settled by them, until safety was at last
secured in the eleventh century in the “inhospitable Chebka.”
Palm gardens were established which for centuries have been irrigated
laboriously by very primitive methods, and the inhabitants have
accumulated wealth in flocks and by barter. The relatively large
population (there were 92,761 inhabitants in 1908), the really great
number of domestic animals, and the great length of time which the
region has been occupied, are all factors of importance in bringing
about a modification in whatever way of the primitive flora.]
[Footnote 21: In 1908, according to the Statistique générale de
l’Algérie, there were cultivated in the territory of Ghardaia
572,114 fruit trees, among which were: almond, 5,850; fig, 101,722;
date palm, 209,898; other sorts of fruits, 211,761. There were also
17,268 hectares of grain under cultivation.]
[Footnote 22: We were informed by our Arab attendant that the kabar,
particularly the fruit, made such animals as ate it insane. The
spicy flavor of the plant might otherwise be distasteful to animals.]
[Footnote 23: Fitting (Die Wasserversorgung und die osmotischen
Druckverhältnisse der Wüstenpflanzen, Zeitschr. f. Bot., 4,
209-275, 1911) states that water-storage tissue is wanting, that
in addition to being large, the leaves are much divided, without
trichomes, and provided with thin cuticle. The stomata are fairly
large, rather numerous, and not sunk. The leaves transpire rapidly
and wilt soon after being removed from the stem. The osmotic
pressure of the cell-sap of the leaves was found to equal 35.3
to 64 atmospheres, from which it is assumed that this plant, like
others growing under desertic conditions, has a root cell-sap of
great osmotic pressure, which permits it to extract water from a
fairly dry soil or at a rather rapid rate. But neither at Biskra
nor elsewhere, so far as I know, does _Peganum_ grow where the
conditions are extreme, as might be concluded from the habit of
the plant as given above.]
[Footnote 24: It has already been shown that the number of days on
which rain may be expected to fall each year is greater at Laghouat
than at Ouargla, and probably at Ghardaia also. According to reports,
the rainy days at Laghouat vary from 20 to 84 (seven years’
observation), with an average of 49 each year. The average number of
days on which rain falls at Ouargla is 14.2. The amount of rain at
Laghouat is 200 mm., at Ouargla 90.2 mm. It would appear, therefore,
that the average rain at Laghouat is less in amount than the average
rain at Ouargla; or, in other words, it points to the torrential as
being the type of the desert storm. Since, other things being equal,
the greater storms would penetrate the ground the most deeply, we may
here have an explanation of the emphasis at Ghardaia on the tap-root
as against the generalized root as the type of the root-system.]
[Footnote 25: The Root Habits of Desert Plants, _l. c._]
[Footnote 26: Compare the root-system of the species at Biskra,
p. 64.]
[Footnote 27: In the vicinity of Tucson (see The Root Habits
of Desert Plants) is to be found a slender-stemmed _Opuntia_
whose roots are fleshy and are placed within 2 to 4 cm. of the
surface of the ground. It has been observed that if the roots are
examined in the midst of a dry season, as in June, they are gorged
with water, but if the soil is removed for a few hours they become
shriveled. A similar habit was seen in another species of the same
genus. Two other genera of the cacti from the Tucson region have
the water-storage organs wholly or partly protected by the soil. In
_Cereus greggii_ the subterranean portion forms an organ 15 to 30
cm. in diameter, and in the other form the fleshy subaerial stem
is partly drawn under the surface of the soil, so that only the
flat upper surface is visible.]
[Footnote 28: In the case of annuals the differences in development
of the shoot between plants well watered and those with only a meager
supply are very striking. In one instance in the Tucson region
specimens of _Parietaria debilis_ growing in extreme conditions,
one moist and the other arid, varied in length between 39 cm. and
8 mm., or a difference with a ratio of 49 to 1. (Root Habits of
Desert Plants, _loc. cit._)]
[Footnote 29: The vegetation in the vicinity of Biskra is so well
known that a sketch will suffice as a basis of comparison with the
flora and conditions of plant life farther south.]
[Footnote 30: Liste des plantes observées aux environs de Biskra
et dans l’Aurés, Trabut _et al._, Alger, 1892.]
[Footnote 31: Briefly the case is as follows (see The root systems of
desert plants, _loc. cit._): _Opuntia arbuscula_ growing near Tucson
develops fleshy roots, but what is probably the same species growing
about 100 miles distant has fibrous roots. Also, seedling opuntias
have fleshy roots. _Opuntia vivipara_, which occurs naturally in
the bottom of an arroyo (oued), may or may not have fleshy roots. By
preliminary series of experiments it was learned that all opuntias
tested which had an abundant water-supply developed fleshy roots,
and it is assumed from this that the differences in this character
as observed in nature had also such a physiological basis.]
[Footnote 32: Eine botanische Exkursion nach Algier and Tunis,
Bericht der Senckenbergischen Naturforschenden Gesellschaft in
Frankfort a. M., p. 76, 1910.]
[Footnote 33: Plants with subterranean water-storage organs—bulbous
plants—are said to be a feature of the High Plateau.]
[Footnote 34: Through Timbuctu and across the Great Sahara, 1912,
p. 266.]
[Footnote 35: Soil samples were taken from the plain about 3
kilometers north of Ghardaia from an area where the vegetation is
relatively good (see p. 40). The surface of the soil at the place
is slightly depressed. Soil samples from the depressed area and
samples from portions of the plain adjacent to it were settled
under water, with the result that the proportion of fine soil was
found to be less in the depressed area. Samples of the soil from
the lower area were placed in air-tight cans and the moisture
content determined subsequently. The soil was found to contain
0.8 per cent water. Through the kindness of the Bureau of Soils,
U. S. Department of Agriculture, the critical moisture-content of
the same soil was determined, which was 5 per cent. The critical
moisture-content of mesa soil, taken from the creosote-bush slope
at the foot of Tumamoc Hill, Desert Laboratory, as determined by
the Bureau of Soils, is 10.5 per cent, which forms an interesting
comparison of nearly similar situations.]
[Footnote 36: The mountains have been disregarded, since in southern
Algeria they are nearly barren. The only exception to this that
I saw was that of the crustaceous lichens in small numbers at
Ghardaia. In the central Sahara, however, where the mountains are
of great elevation, the mountain climate brings about favorable
conditions for plant life.]
[Footnote 37: Die Wasserversorgung und die osmotischen
Druckverhältnisse der Wüstenpflanzen. Zeitschr. f. Botanik,
4, 1911.]
[Footnote 38: Hayward, _loc. cit._, p. 320, says that at In
Salah camels are driven 200 kilometers before finding suitable
grazing-grounds.]
[Footnote 39: It should be understood that such densely populated
areas are separated by wide stretches where are few or no plants.]
Transcriber's note:
pg 15 Added period after: vegetation of the country
pg 17 Changed: _Quercus bollota_ to: _ballota_
pg 24 Changed: _Rhus oxycantha_ to: _oxyacantha_
pg 25 Changed: _Artistida pungens_ to: _Aristida_
pg 32 Changed: Astericus pygmæus to: Asteriscus
pg 35 Changed: _Petama spherocarpa_ to: _Retama sphærocarpa_
footnote 21 (pg 38) Changed: Statique to: Statistique
pg 43 Changed: were in in pre-M’Zabite to: were in pre-M’Zabite
pg 43 Changed: iteslf to: itself
pg 50 Changed: _Zillikoferia_ to: _Zollikoferia_
pg 53 Changed: Fig. 441. to: 44.
pg 54 Changed: _Astericus graveolens_ to: _Asteriscus_
pg 55 Changed: _Tragonum nudatum_ to: _Traganum_
pg 56 Changed: _Phargmites_ to: _Phragmites_
pg 57 Changed: Maricandia cinerea to: Moricandia
pg 57 Changed: Haloxylon articulata to: articulatum
pg 57 Changed: Sorzonera nudulata to: Scorzonera undulata
pg 59 Changed: P. albans to: albicans
pg 63 Changed: _Ferula visciritensis_ to: _vesceritensis_
pg 65 Changed: _Ferula vesciritensis_ to: _vesceritensis_
pg 73 Changed: edaphacic to: edaphic
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