104 THE POPULAR SCIENCE MONTHLY. 



general appearance and habits, but absolutely devoid of thorns or 

 prickles. The leaves, indeed, are toothed and pointed, but the points 

 never project into fierce spines, as in the more advanced kinds ; and 

 even the little scales that form a cup for the flower-head, though 

 faintly stiff and sharp, are scarcely if at all defensive in character. 

 The flower, of course, is usually the first part to be specially protected, 

 because upon it depend the future seeds and the hope of coming gen- 

 erations of thistles. Just as instinct teaches female animals to fight 

 fiercely and bravely for their young, so natural selection teaches men- 

 aced plants to arm themselves stoutly against the threatening depre- 

 dators of their seeds and blossoms. The reason why the saw-wort and 

 its unarmed South European allies have managed to do without the 

 protective inventions of their more developed relations is no doubt 

 because they live mostly in thickets and woody places, not much over- 

 run by cattle or horses. Their neighbors in the open meadows and 

 pastures have been compelled long since to adopt more military tactics 

 in order to save themselves from premature extinction. Often, indeed, 

 in a close-cropped paddock, you will find only two kinds of tall plant 

 uneaten by the beasts — the meadow buttercup, preserved from harm 

 by its acrid juices, and the creeping thistle, armed all round with its 

 long rows of parallel prickles. 



In the mountains of Wales and the north of England there is yet 

 another kind of true thistle, classed as such by technical botanists (for 

 the saw-wort is artificially relegated to a distinct genus), which is also 

 destitute of prickles on the leaves, though it sometimes shows the first 

 faint beginnings of a prickly tendency around the scaly flower-cup, and 

 in the bristly teeth of its crinkled leaves. From this early stage in 

 the evolution of thistledom we can trace the gradual steps in the de- 

 fensive process, through thistles that grow with prickly leaves, and 

 those in which the prickly margins begin to run a little down the 

 stem, to those which have clad themselves from top to toe in a perfect 

 mail of sharp spines, so that it becomes quite impossible to grasp them 

 anywhere with the hand, and they can only be eradicated by the hoe 

 or plow. It is a significant fact that the most persistent and trouble- 

 some of all these highly developed kinds, the creeping thistle, now 

 universally diffused by man over the globe, is a special weed of culti- 

 vation, far most frequently found in tilled fields, and seldom disputing 

 with the simpler forms the open moors, mountains, or pastures. It 

 does not trust entirely, like others of its kind, to its floating seeds, 

 blown about everywhere as they are by their light tag of thistle-down; 

 but it creeps insidiously underground for many yards together, send- 

 ing up from time to time its annual stems, and defying all the attempts 

 of the agricultural interest to exterminate it bodily by violent meas- 

 ures. This is the common and familiar pale purplish thistle of our 

 English corn-fields, and there can be little doubt that it has developed 

 its curious underground habits by stress of constant human warfare, 



