1903.1 



KNOWLEDGE. 



163 



themselves (Carduus, Cniciiii, Oiiopordoii, Carlina) are 

 among the most perfect examples to be met with in our 

 flora of defence against grazing animals. The beautifully- 

 cut leaves are fringed with an array of spines of wonderful 

 sharpness ; the stems have often wings similarly armed ; 

 the leaves of the involucre end each in a spine likewise, 

 sometimes of quite terrifying size, as in the Milk Thistle 

 (Sili/hmn Mariar.uni) . Were it not for this impenetrable 

 armour the plants would early fall victims to herbivores, 

 for the stems and leaves are juicy and sweet. The most 

 perfectly protected of our native species is perhaps the 

 little Carline Thistle ; for the botanist who desires a 



Fro. 4.— Cai-liiie lliistle (Carlina imlyaris). (Half natunil size.) 



specimen, the only method of securing one with an 

 ungloved hand is to get down under the ring of basal 

 leaves and grasp the strong tap-root. This species is also 

 remarkable among Mritish Thistles for the dry and woody 

 nature of every j'art of the plant, which preserves its form 

 unchangeil it' withered, so that one may even find in a 

 sheltereil s|iot a last year's and a this year's plant standing 

 side l)y side, the former bleached and battered, but un- 

 changed in form of leaf and flower. 



Most of our Thistles are biennial herbs, forming in their 



first year a large rosette of spiny foliage, often of great 

 regularity and beauty, and in their second year, shooting 

 up, flowering, fruiting, and dying. A few species, however, 

 notably the too common Field Thistle (Cnicus arvensis), 

 have underground creeping stems. The stems of the 

 Field Thistle plunge so deeply into the soil, grow so 

 rapidly, and are so brittle and tenacious of life, that it is 

 one of the most troublesome of all our weeds. The deeply 

 lobed and spiny leaves of the Thistles are often coarsely 

 hairy, but sometimes smooth and shining; in the Milk 

 Thistle they are variegated by having the veins picked out 

 in pure white. The leaves are often assisted in their func- 

 tion of assimilation by the leaf-like spiny wings which run 

 down the stems, and protect theru from injury. Almost 

 all our Thistles furnish beautiful examples of pai'aehute- 

 fruits. each fruit being crowned with a spreading ring of 

 delicate hairs, o£ which each one again bears a ronr of 

 smaller hairs down each side Suspended l)?low this 

 delicate framework the seeds are borne to long distances. 

 Passing by the genera SerratnH and SaiiKsurei, each of 

 which has but a single British representative, we come to 

 the Knapweeds (Cent iiirga), which may chiefly claim 

 attention here on account of the interesting varietv which 

 they offer in the fonn of the involucral leaves. Those of 

 the Black Knapweed are familiar to every child whose 

 luck it is to live ia the country — curious little dirk-brown 

 objects, remarkably resembling certain small animal forms 

 which even naturalists are generally glad to avoid. In 

 other species they are yellow and chaffy. In O. sohtitialis, 

 St. Birnaby's Thistle, on the contrary, the phyllaries 

 end in long slender spines, while in the Star-Thistle 

 (C Calcitrapa) the spines are much larger, stronger, and 

 spreading, guarding the flower-heads like an array of 

 bayonets. Another interesting point about the Knap- 

 weeds is that they show sometimes a differentiation in the 

 structure and function of the flowers, as we have seen in 

 the Corymhiferw. This is best exemplified in the Blue- 

 bottle (C. Cyanus), which brightens our corn-fields with 

 stars of brilliant blue in autumn. The blue colour is 

 derived entirely from the outer ring of flowers, which 

 consist merely of brilliant corolla, the centre being occupied 

 by numerous small close-set purple perfect flowers, which 

 benefit by the visits of insects which the brilliance of the 

 barren ray-flowers induces The Great Knapweed ( C. 

 Scabiosn) shows a corresponding division of labour. The 

 Black Knapweed (C. niiji-<i) has apparently not yet made 

 up its mind whether to go in for a ray or not. Normally 

 the flower- head consists of a solid disk of fertile flowers, 

 but rayed forms ai'e constantly to be met with. 



Lastly we have the Dandelion group, or Lujulijlorie, 

 represented by a dozen genera, most of which agree iu 

 having yellow heads oC flowers closely resembling those of 

 the Dandelion. The character of the group lies in these 

 flower-heads, which are made up entirely of ligulate perfect 

 flowers, in shape like the ray-flowers of the Daisy group. 

 Thoy are likewise distinguished by their milky, often acrid, 

 juice. Only two of the British representatives of the group 

 have flowers which are not yellow. These are the Chicory 

 {Cichorium Intybus), whose large light blue flower-heads 

 are such a delightful feature in sandy fields or on dry 

 banks; and the Blue Sow-Tiiistle {Mulyeiiiim alpiniim). a 

 handsome alpine plant, attaining a height of several feet, 

 found on lofty mountains in a few localities iu Scotland. 

 One other not -yellow member of the Liguli/tone finds a 

 ])lace in British Floras, though not a native, namely, the 

 Salsify (Traijupofion porrifoliii^), which has naturalized 

 itself in meadows in many places, being originally grown 

 in gardens for the sake of its fleshy roots, which resemble 

 Asparagus in flavour. This plant has heads of bright 

 purple florets, which, like its near yellow-flowered relative. 



