THE DISPERSAL OE SEEDS. 
posita3 are developments from the mari,nn of the calyx-tube. In connec- 
tion with these last-mentioned plants, i would remind you that we have 
some Compositie with a trace of a limb to the calyx and many without 
any pappus ; whilst, when present, the pappus may be sessile at the 
apex of the t'ruitlot, as in the Thistles, or carried up on a long, slender 
stalk-like tube, or " stipes," as in the Dandelion ; and its hairs may be 
simple (pilose) or feather-like (plumose). The hygroscopic character of 
these hairs gives them some effect in levering the fruitlets oft" the 
common receptacle, in connection with which action I would also remind 
you of the remarkable change of form of the common receptacle in the 
Dandelion (Taraxacum) from concave in the flowering stage to a taut 
convexity when in fruit. The tufts of hair in the Reed-mace (Typha) 
proceed from the pedicels ; whilst the well-known long tale-like plumes of 
the Feather-grass (Stipa pennata, L.), one function of which, as Dr. 
Francis Darwin has demonstrated, is to bury the fruit in the ground, are 
awns proceeding from the apices of glumes. 
Among seeds the presence of a " coma " is sometimes general in large 
groups of plants, as in Salicinas, Apocynacea?, and Asclepiadaces. It 
may spring from the base of the seed, as in Popiilus and Salix ; from its 
apex, as in Epilobiiivi, Tamarix, and Strophanthus ; from both ends, as 
in another African Apocynad, Adenium Hongel, A. DC. ; or from the 
whole surface, as in the Cottons (Gossypimu). It is interesting to note 
that the long beak to the seed of the South African Strophanthus hispidus, 
crowned with a delicate plume of hairs, is reproduced in some of the 
epiphytic Tillandsias (Bromeliace^e) of Tropical America ; and Sir John 
Lubbock calls attention to species of the asclepiadaceous uEschynanthus 
in which there are only three hairs on each seed — one at one end and two 
at the other — but these being very flexible are capable of wrapping round 
the wool of an animal, so aiding dispersal otherwise than by wind. 
This brings me to the last main division of dispersal mechanisms, 
those dependent upon animal agency. These fall mainly into two groups, 
those adapted for outside carriage — viz. burrs and hooked structures 
and those adapted for inside carriage, most of which are succulent, and 
many of them brightly coloured. To the former of these two groups it 
has been stated that ten per cent, of our flowering plants belong. In the 
first group it is noteworthy that no burrs occur on aquatics or on plants 
over four feet in height, such species being obviously out of the way of 
w^oolly or hairy animals. Seeds are seldom furnished with hooks, but 
such appendages may occur on bracts, calyx, style, or pericarp. The 
nyctaginaceous genus Pisonia is not bristly, but its persistent bracts, or 
" anthocarp," are so glandular as to cling to bird's feathers. Mr. H. 0. 
Forbes relates that on Keeling Island the fruits adhere in this way to the 
feathers of herons in such quantities as to cripple or even kill the birds. 
In the North American Grass Cenchrus tribuloides, L., the fruit is enclosed 
in a hard, prickly involucre of sterile spikelets which renders this species 
a troublesome pest in wool-growing districts. Still more striking is the 
case of the composite Xanthium spinosum, in which the fruits are 
enclosed in a hard woody involucre covered with prickles. A native of 
Russia, it was introduced in 1828 into Wallachia in the manes and tails 
of Cossack horses. Similarly it travelled with cattle and wool by way of 
