2932 REV. G. HENSLOW ON THE ORIGIN OF PLANT-STRUCTURES 
VI. Protection of Buds. 
A feature very characteristic of the African desert grasses 
may be here mentioned—namely, the retention of the leaf-sheaths, 
so that the annual buds are carefully protected against drought 
when they appear in the spring. Similarly the Paronychiacee 
are provided with scarious stipules completely concealing the 
buds within them. Similarly Lavandula atriplicifolia has a spike 
of densely overlapping bracts (resembling the “ wheat-eared ” 
monstrous form of Dianthus) protecting the flower-buds. M. 
Warming noticed the same thing in Brazil. He thus writes :— 
“ Dans le groupe des Glumiflores (Cypéracées et Graminées) les 
feuilles sont étroites et raides; presque toutes les espéces de ce 
groupe sont tuniquées au sens ou M. Hackel a employé ce mot 
pour la premiére fois en 1889, c’est-d-dire que les bourgeons 
demeurent enveloppés et protégés par la base des feuilles qui 
persistent pendant longtemps, comme cela a lieu aussi dans le 
Posidonia oceanica (Andropogon, Rhyncospora, Scirpus sp., etc.).” 
In the African deserts numerous species of Aristida illustrate 
this fact. Lastly, it may be added that bulb-scales may become 
almost “woody ” (Allium Crameri, &c.). 
VII. Roots. 
The organs hitherto considered are mostly above ground, but 
roots also exhibit features of self-adaptation to desert life in 
the enormous length they sometimes attain. Dr. G. Volkens 
describes * how a young plant of Monsonia nivea of one year’s 
growth may be seen between July and January to have a small 
rosette of three or four leaves, while the roots may be twenty 
inches in length. Other plants may have roots two or more 
metres long. The Colocynth, he observes, has an enormous length 
of root in order to maintain its existence. It stands singly, has 
large herbaceous leaves without any means of preventing an 
excess of transpiration, as a cut shoot fades within five minutes ; 
and yet it flourishes unshadowed through the whole summer. 
The great length of root in certain desert plants has been also 
noticed elsewhere. Thus Dr. Aitchison observed in Beluchistan 
that “several of the Astragali (A. kahiricus, auganus, buchtor- 
mensis) have long whip-like roots, the bark of which is employed 
as twine by the people. These roots are extracted in a very 
neat way, by attaching a loop of twine to the crown, passing a 
stick through the other end and making it act as a lever ” t. 
* Op. cit. p. 7 [supra, p. 220]. t Op. cit. p. 431 [supra, p. 221]. 
