1.We sometimes hear of animals that have becomeextinct，such as the great auk，the last specimen ofwhich was shot during the present century.Plants，too，run the risk of becoming extinct in certain districts.When a rare plant is found in some nook among themountains，botanistsare so eager to get a specimenof it that sometimes not a single plant is left.There is no danger of our cultivated plants becoming extinct，however，for farmers take care to preserve a sufficient quantity of seed every year.
2.The lower animals are not so intelligent as to preserve or cultivate the plants on which they feed.
Where animals of the graminivorous or browsingtypeare plentiful，therefore，their feed-plants run the risk of being eaten up entirely，while they are young and juicy，and before the seeds of another crop have been sown.
3.Plants have therefore to rely on certain means of self-defence，in order that they may live their lives and sow their seeds，instead of being eaten up bodilyby the first grass-eating animal that happens to pass.Those that have no means of self-defense will naturally be eaten up first，while those with the best weapons or the toughest armour will live longest and produce most seed，and so will spread most widely over the ground.
4.The ways in which plants protect themselves from animals are often most ingenious and effective.Some plants contain a poisonous juice，and if an animal does not take warning from its taste or smell，his attack on the plant will cost him his life.A few poisonous plants grow in this country-the deadly nightshade，the water-hemlock，andothers；and children have sometimes been poisoned by eating such plants.There are others，such as water-cress，which we find very good to eat，but which aretoo bitter for animals to feed on.
5.It is a curious fact that the deadly nightshade，which is so poisonous to the browsinganimals that might otherwise eat it all up，is quite harmlessto beetles and smaller creaturesthat live on it.The plant can easily spare as much of its leaves as they require，and they seem rather to like its juice.Animals appear to detect poisonous plants by their smell，though there are some of them which to us have no smell at all.
6.Next to poisonous plants we might place sting-ing plants，such as the nettle.The leaves of the nettleare studdedwith fine hollow hairs，rounded at the tip.
When one of these hairs is touched，its round point breaks off，and its sharp，ragged edge pierces the skin，while the juice which filled the hollow flows into the wound.The sting of some of the huge tropical plants of this kind is nearly asdangerous as the bite of a poisonous snake.Yet the nettle can hardly be called poisonous，for the young s h o o t s a r e s o m e t i m e s used as food，and taste a little like spinach when they are boiled.
7.The most common means of defence among plants are thorns，spines，prickles，or bristles of various kinds，some of them very strong and dangerous-looking，others just sharp enough to be unpleasant for any animal that may bein questof a meal.We have all come in contact withsuch plants as thistles at one time or another，and we have found that they defend themselves very well.Yet the donkey can make a meal of them in spite of their spears.
8.Thistles have both stem and leaves covered with prickles.Other plants，such as the hawthorn and blackthorn，have them on the stem or branches only，and the young lea vesspring up under shelter of these thorns.Certaingrasses and sedgeshavetheir prickles set on the leaves themselves，which are so hard and jagged at the edges that most animals leave them alone.
9.The furze has so many thor ns that we hardly notice anythingelse to be protected；but there is a family of plants，called the cactus，that has gone still further in the way of self-defence.They are found in the desert，where plants are scarce，and even the roughest and least juicy are in danger of being eaten up，if they do not die ofdrought.But the cactus remains juicy and green inspite of either heat or animals.
10.Its leaves have turned into mere prickles，hard，sharp，and dangerous to touch，without any of that soft green surface which is necessary to the life and growth of a plant.The stem，on the other hand，is covered，not with bark，but with that green surface which is found on the leaves of other plants.The stem has undertaken the work of the leaves，seeing that the leaves have had to undertake the work of defence against animals；and so the plant thrives where hardly any other vegetable life is found.
11.After all，plants do not carry on war againstanimals；they act only in self-defence，and have nomore armour than is absolutelyneeded.You may seethis by looking at the next holly tree you pass.If it is a tall one，you will notice that while the lower leaves that are exposed to danger are sharp and prickly at the edges，those on the higher branches are smoothand unprotected.This fact about the holly tree hassuggested the poem by Southeyas your next lesson.
THE HOLLY TREE
1.O reader！hast thou ever stood to see The holly tree？
The eye that contemplates Its glossy leavesit well，perceivesOrdered by an Intelligence so wise.
2.Below，a circling fence，its leaves are seen Wrinkled and keen，-No grazing cattle through their prickly roundCan reach to wound；But as they grow where nothing is to fear，Smooth and unarmed the pointless leaves appear.
3.I love to view these things with curious eyes，And moralize ；And in this wisdom of the holly tree Can wisdom seeWherewith，perchance，to make a pleasant rhyme-One which may profit in the after-time.
4.Thus，though abroad perchance I might appearHarsh and austere ；To those who on my leisure would intrude，Reserved and rude；-Gentle at home amid my friends I‘d be，Like the high leaves upon the holly tree.
5.And should my youth，as youth is apt，I know，Some harshness show，All vain asperitiesI day by dayWould wear away，Till the smooth temper of my age should be Like the high leaves upon the holly tree.
6.And as when all the summer trees are seen So bright and green，The holly leaves a soberhue display，Less bright than they；But when the bare and wintry woods we see，What then so cheerful as the holly tree？
7.So serious should my youth appear among The thoughtless throng；So would I seem among the young and gay More grave than they；That in my age as cheerful I might be As the green winter of the holly tree.