112 JOURNAL OF THE EOYAL HORTICULTURAL SOCIETY. 
growing V. odorata and V. Jiirta ; but an arrangement somewhat similar 
obtains in the Box {Buxus). 
The third class of sling-fruits, that in which the valves of the drying 
fruit become spirally twisted, though represented by the genus 
Ahtra'ineria among Liliacere and in other natural orders, is characteristic 
especially of the Leguminos^e and Euphorbiace^. Most of us have 
noticed on a hot summer's day the explosion of the dry pods of Broom or 
Furze, often accelerated by contact with us as we walk past, and a similar 
spiral coiling of the two halves of the legume occurs in Vicia, Orobus, 
Latliyrus, Lupinus, Wistaria, Indigofera, Bauhinia, and others. 
Bauhinia purpurea, for example, is recorded as throwing seeds weighing 
2-5 grammes to a distance of 15 metres. This remarkable torsion is the 
result of the drying of a layer of thick-walled elongated cells which lies 
diagonally across each valve. In the Euphorbiacea?, such as Mcrcurialis, 
Euphorbia, and Bici7ius , the valves being shorter, the spiral torsion is less 
obvious ; but we have in this group another of the best known instances 
of explosive seed-dispersal, that of the Sandbox-tree, or Monkey's Dinner 
Bell of Tropical America {Hura crepitans, L.). Certain layers in this 
large fruit contract with such force in drying as to shatter the entire 
fruit, bursting violently even through strong enclosing substances, and 
throwing the light seeds to a considerable distance. 
We come next to the third main division of our subject — the adapta- 
tion of fruits and seeds to dispersal by wind. This may be roughly 
divided under three categories : 1st, lightness, whether of the seed, fruit, 
or entire plant ; 2nd, wrings ; 3rd, plumes or parachutes. It is un- 
doubtedly significant that it is especially among parasites and saprophytes 
— plants that more urgently require a wide dispersal of their abundantly 
produced seed — that we meet with some of the most striking instances of 
extremely light seeds. Orobauche, Monotropa, Pyrola, and many Orchids 
are cases in point, Goodyera repens, for example, having seeds which 
weigh only -000002 gramme each. Small light seeds are also often com- 
bined with the somewhat simple adaptation Imown as censer action, as in 
many Caryophyllaceae, Poppies, &c. The inflated pods of the Bladder Senna 
(Colutea arborescens, L.) may merely catch the wind while still on the 
plant, so as to jerk out the seeds separately as they sway in the breeze, 
or they may break off and be carried balloon-like to somewhat greater 
distances. As w^e might expect, it is especially among the plants of those 
wide-stretching level tracts of arid ground, the Steppes of Eastern Europe 
and of Asia, where plants have often so great a difP.culty in sustaining 
life at all that we meet with instances of this class of adaptation. The 
fruit of Cachrys alpina, MB., one of the Umbelliferae of these regions, for 
example, measures 13 mm. by 10 mm., but weighs only '07 gramme, whilst 
another species of the same genus, from Shiraz , measuring 1 5 mm. by 10 mm . 
weighs only "06 gramme. The spirally coiled legumes of some species of 
Medicago may also be cited in this connection ; but more interesting still 
are those cases in which various subsidiary structures become detached, or 
even the whole plant is rolled away by the wind. In Trifolium subter- 
raneum, L., and allied species, for example, the calyx-teeth of the 
abortive flowers form a loose globular cage round the head of legumes, 
and the whole of the ball thus formed breaks oft' and is rolled along by 
