THE CONDITIONS FOR THE DISTRIBUTION OF PLANTS. 107 
which is due to the absence of a particular insecb which abounds 
in the native country of the Vanilla. A still more interesting 
example is afforded by the rust of the wheat, caused by a species 
of fungus, Puccinia graminis, which in order to survive must ger- 
minate on the leaves of the Barberry, where the fertilisation is 
performed. This fact was first observed by the late Danish Professor 
Oersted, and has been practically corroborated by the good 
results of almost eradicating the common Barberry in Denmark, 
where it was formerly very frequent. Similar mutual relations 
between plants are common among several other species of fungus. 
The most important assistants to fertilisation are wind, dew and 
insects, and rarely water. 
Having now mentioned the most important conditions for the 
distribution of plants, I shall proceed to deal with the means by 
which it is performed. 
The most natural way of propagation of plants is by seeds, and the 
different agents that assist in spreading or distributing these are 
wind, water, animals, birds, insects, and plants themselves. 
The most active of these agents is the wind, and very frequently 
fruits and seeds are specially fitted to derive the full advantage of its 
action. As examples I shall mention the feathery tailed fruits of 
“ Trayeller’s joy,” of which at least one species, Clematis Gouriana, 
is common in our jungles; in this case the elongated styles serve 
as appliances for flight; or the pappus of most of the com- 
mon Composite; beautiful, feathery, in the now common, but 
originally introduced T'ridax procumbens, or-hairy in Blumeas, 
Vernonia cinerea, Emilia sonchifolia and many other common 
weeds. Here the calyx or the outer perianth of the florets 
is adapted for flight. Hairy appendages of other kinds, comas, 
are frequent on seeds of several Asclepiads, as Calotropis 
gegantea, Asclepias curassavica, Cryptostegia grandiflora, and in 
many Apocynes as Anodendron paniculatum, Dr. Macdonald’s seed- 
traveller, &c., and in a great many other plants. The hairy 
appendages of seeds in the cotton-plants, Gossypium, in silk 
cotton trees, Hriodendron anfractuosum and Bombax malabaricum 
Serve a double purpose, ¢. g., as appliances for flight and as a means 
of adhesion to the skin of animals. Other appliances for flight 
are the winged fruits and seeds, as of Combretum, Terminalia 
glabra, the “ Ain,” which on account of its 5-winged fruit has been 
ealled Pentaptera, Hiptage Madablota, many other Malphigiacee, 
