COMPOUND FLOWERS 161 



the attention of the most casual observer. This appendage to the scales of 

 the involucre procured for the plant its specific name, for it much resembles 

 the implement used in ancient warfare, and called Caltrop, which was an iron 

 ball set with iron spikes, and which, being thrown beneath the feet of the 

 horses, cruelly wounded these animals as they pressed onwards. 



8. Yellow Star Thistle (C. sohtitiaUs). — Spines of the upper involucral 

 bracts half an inch long, not channelled ; spines of the lower bracts very 

 small. Stem winged, erect, rigid, and branched, each branch terminated by 

 a flower-head. I^ower leaves lyre-shaped, upper very slender with entire 

 margins. Plant annual. This plant, Avhich is a native of the Mediterranean 

 region, appears to have been introduced to the South and East of England 

 among seeds of lucern and other fodder plants. It occurs only rarely in the 

 districts indicated, and may be readily known from the other species by its 

 winged stem, a foot or so high, and its yellow florets. The flowers appear 

 from July to September, and are succeeded by copious white pappus. 



Sub-Order III. Corymbifer^. 



1. The Tansy Group {TuUflorce). 



24. Bur Marigold {Bidens). 



1. Nodding Bur Marigold {B. c&nua). — Leaves sessile, lanceolate, 

 undivided, connate ; flowers drooping ; bracts longer than the involucre ; 

 fruit usually with 3 or 4 bristles ; annual. The sides of streams and rivulets 

 are the spots on which we must look for this plant. It is not, however, 

 very ornamental to them, for the large button-like flowers are of a tawny- 

 brown or yellowish-green colour, having at their base a number of leafy 

 bracts. The stem is one or two feet high, and somewhat succulent, as are 

 the large smooth leaves. The oblong fruit terminates in stiff bristles, which 

 are three or four in number, and each of which, as may be clearly seen by a 

 glass, is turned back like the point of an arrow, so as to cling to the wool of 

 an animal, the clothing of man, or any other object with which it may come 

 in contact. Dr. George Johnston, in his " Flora of Berwick," furnishes us 

 with some very interesting comments on this plant. "The following 

 remarks," says this writer, "were communicated to me by Mr. Brown: 

 'Annual plants, it has been observed, produce in general more seed than, 

 perennial, and the reason is obvious. The Bidens is annual, and we might 

 expect it to have the benefit of this provision ; for, indeed, the circumstances 

 of its growth seem to call for greater productiveness than is common even 

 among annuals. It is found by the sides of ponds and ditches, and its seeds 

 are thus ever in danger of being blown either to the dry land, or to the 

 deeper parts of the pond. In either case they must perish. On the dry land 

 they are useless, for it is a water plant ; and, on the other hand, if blown to 

 the deeper parts, they will sink to the bottom, and never germinate, or ger- 

 minate in vain. Now, though these seeds are exposed to so many dangers, 

 and though the continuance of the species depends on their preservation, yet 

 is their number by no means great. The flower-heads are small, and never 

 numerous ; the seeds large in proportion, and, of course, few are produced by 



II.— 21 



