1887] The Milkweeds. 607 
these claws have been acquired in the course of‘ ages, being 
developed more and more fully as time went on. Neither can 
there be any doubt but that they are now necessary for his 
existence. So it is with all other weapons of defence or offence 
that have been developed by use. Their principal purpose has 
been to enable their possessor to live, and, as the strongest and 
the one best provided with good weapons is the one most likely 
to continue his kind, improvement goes on until-a certain degree 
of perfection is attained, and the animal is fitted to a place which 
it holds against all competitors. 
_ While adaptations of one kind arise among animals to nasii 
ther to compete with each other in this struggle, adaptations 
of another kind are developed in the plant world. These take 
the form of hairs on the stems and leaves; stronger modes of 
growth; climbing propensities ; parasitic habits ; the development 
of prickles or thorns; the formation of deleterious juices, un- 
pleasant odors, or aromatic qualities. Others, again, place their 
chief reliance for continuing their species on the hard shell en- 
casing their nuts or fruits, and, by producing these in enormous 
numbers, have an excellent chance of perpetuating themselves. 
All these have, it should be understood, been acquired by plants 
so they can hold their ground in the battle for life; and, conse- 
quently, those species best provided with means to -resist the 
attacks of animals, either by being more unpalatable through. 
disagreeable odors or tastes, or by having tougher or harder 
‘shells to the seeds, or by being aromatic, or in some other way, 
will stand the best chance of living long enough to perfect seed, 
and thus be the means of continuing their kind. 
Each one of the many ways of resisting the attacks of ani- 
= mals has been only gradually acquired. From a small begin- 
_ ning, the importance of which is not at first to be perceived, the 
features have increased in usefulness and attained perfection only 
after many severely fought battles with hardy antagonists. 
Perhaps one of the most effectual of all the modes of protec- 
tion acquired by plants is to be found in the presence of a milky — : 
or colored juice. This is a character which is shared in com- 
mon by a great number of species of widely different orders; 
but there is no species in which the milky juice is more con- _ 
spicuous than in the Milkweed. While in various species of : the - 
: pemposte, such as the Dandelion, the Wild a out oe 
