THE DlsrEliSAL UE .SEEDS. 
113 
wind. In tlio Wig tree (Ilhus Cotliius, L.), a familiar garden shrub, most 
of the branches of the inllorescence are barren, forming merely reddish 
feathery arms, one branch which bears a drupe becoming detached 
together with all this *' wig," and being in consequence readily blown 
about. Similarly in the Australian grass Sjnnifex aquarrosus the entire 
head, the bracts of which are long and spiny, breaks off when the fruits 
are ripe, and is blown about in the sand. The Eose of Jericho 
{Anastatica hicroclmntica, L.), one of the Cruciferic, which is now 
commonly sold as a curiosity in London, is a type of those Steppe plants 
which become detached whole from the ground during the arid fruiting 
season, when the soil is cracked by heat. Its branches, bare of leaves 
but still carrying the fruits, bend inwards, forming a dry ball of wicker- 
work. This inward bending may help to uproot the tap-root, as does 
the outward bending of the branches in the case of a physiologically 
similar plant, Planiago cretica, described by Kerner. The whole plant is 
then blown along until it reaches moisture, when both branches and 
fruit- valves open out hygroscopically. It has been suggested that this 
plant is the G algal " of Psalm Ixxxviii. Vd, translated " wheel " in our 
English Bibles. There are also a considerable variety of herbaceous 
plants on the Russian steppes, of which AlJiarji canielorum, Salsola Kali, 
and Centaurca diffusa — plants belonging to very divers families — may be 
mentioned as examples, in which the base of the aerial stem decays, so 
that all the rest of the plant is liberated. These dry, rigid, branching 
plants are rolled together by wind until they accumulate in the huge balls 
known as steppe-witches or wind-witches.* 
We come next to the great series of plants in which wind-dispersal is 
facilitated by wing-like structures attached either to fruit or seed. 
Among these we shall find representatives of a very large number of 
natural orders and a great variety in the anatomical or structural origin 
of the " wing " itself, showing that this mode of seed-dispersal has 
originated independently in many different groups, and has been evolved 
along many independent lines. Nevertheless, as Sir John Lubbock has 
pointed out, they agree in many, physiological or adaptational characters ; as, 
for instance, in occurring almost always on trees or climbing shrubs well 
exposed to wind, and in having the seed generally in an eccentric position. 
Beginning with those wings which are attached to fruits, we find that 
w^e may further subdivide them into three or four groups. In some the 
wing is in origin a bract, as in the Hop {Humulus Lupidus, L.), the Hop- 
hornbeams (Ostrya), the Spinach (Sirinacia), and in such members of the 
order Nyctagineae as Boitgai)ivillea,v;heve the bract has previously served 
to attract fertilising insect-visitors, and Mirahilis. Here, too, we must 
class the numerous Grasses, such as species of Briza and Melica, in which 
glumes adhere to the fruit and serve more or less as wings. Here, too, 
belongs that beautiful structure, the adherent leafy bract in the Lindens 
(Tilia), to which the weight of several fruits is so eccentrically attached 
as to give it in falling the same screw-propeller action that we have in the 
wings of Maples — an action which enables a very slight breeze to carry it 
beyond the over-shadowing of the parent tree. 
Next we have a variety of instances of wings originating in the 
* - Kerner, Natural Histprij of Plants, English edition, vol. ii p. 850. 
