218 



THE YOUNG NATURALIST. 



in length, deeply cut and jagged, each 

 lobe terminating in a hard, sharp, 

 needle-like spine a good half-inch long 

 The stout stem and branches are simi_ 

 larly armed at all points, for the bases 

 of the prickly leaves run down the 

 stem and form interrupted wings at 

 the angles, the whole plant being cov- 

 ered with an impenetrable armour of 

 pointed spears, sharp and keen as 

 needles. So formidable are these de- 

 fences as to render it well nigh invul- 

 nerable to browsing animals, the 

 patient and longsuffering donkey alone 

 being said to relish its prickly flower 

 heads. But when the patient " moke " 

 meditatively munches the musty mor- 

 sel there is a suspicion that it is a case 

 of Hobson's choice, and that it is his 

 needs and not his taste that influences 

 him. To further protect the thistle 

 from the predatory attacks of crawling 

 insects, the whole surface of the stem 

 and leaves is covered with a dense 

 downy pubescence, and the prickly 

 scales of the flower head are interlaced 

 with a silky substance, as if a spider's 

 web had been spun over it, hence the 

 technical term arachnoid is used for 

 this covering, the meshes of which 

 form an effective barrier. 



The thistle belongs to the natural 

 order Composite, numerically the 

 largest and most universally distributed 

 order of plants on our globe. In this 

 country it is only represented by herba- 

 ceous plants, but in the tropics many of 



its members assume the dignity of trees 

 with permanent woody stems. All 

 the Composite are characterised by 

 having an immense assemblage of 

 small individual flowers aggregated 

 together, enveloped and protected by 

 less or more numerous scale-like leaves 

 forming an involucre. The dissection 

 of the flower head of our humble 

 thistle forms a very good illustration 

 'of one of the types of the order in 

 which all the florets are similar in 

 shape and function. Yiewed as a 

 whole the flower head closely resembles 

 a paint brush, the numerous purple 

 florets extending beyond the many 

 rows of prickly bracts of its involucre. 

 If the flower head be cut through 

 longitudinally, a firm, flattened rather 

 succulent portion (the receptacle) is 

 seen, on which all the florets are seated 

 as closely packed as possible, but each 

 one surrounded with numerous feathery 

 hairs. These are similar in structure 

 to the familiar "thistle down," but 

 they take no part in the dispersion of 

 the seed, and after the thistle fruits 

 are all scattered far and wide they still 

 remain adherent to the receptacle so 

 that their function is not very obvious. 

 Removing and examining an individual 

 floret which is complete in itself, the 

 smooth, compressed, oblong body at 

 the base is the ovary, which when 

 mature contains a solitary seed. Sur- 

 mounting it is the calyx, transformed 

 into a fringe of feathery hairs, in its 



