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.