108 THE POPULAR SCIENCE MONTHLY. 



vast previous evolutionary history. Starting apparently from blossoms 

 ■with five distinct and separate yellow petals, like the buttercups, the 

 ancestors of thistlehood gradually progressed, as it seems, by insect 

 selection, to a condition something like that of the harebell or the Can- 

 terbury bell, in which the petals have coalesced at their bases into a 

 single large and united tube. Clustering together next into closely 

 serried heads, like those of the scabious, the rampions, and the com- 

 mon blue sheepsbit, they endeavored to make up for the individual 

 minuteness of their dwarfed flowers by the number and mass collected 

 in a group on the summit of each stem. In this way they gradually 

 assumed the distinctive crowded composite form, each floret consisting 

 of a tubular five-lobed corolla, a calyx reduced to hairs or down, and 

 single tiny seed-like fruit. Of this stage in the development of the 

 family, the simpler and less specialized members of the thistle group, 

 such as the unarmed saw-worts and the Alpine saussurea, are now the 

 best surviving representatives. From some such early central form, 

 the evolving composites split up and diversified themselves into all 

 their astonishing and almost incredible existing variety. Some of 

 them, varying but little in minor details from the parent stock, ac- 

 quired prickly leaves and grew into the thistle kind, or developed 

 hooked and sticky involucres, and were known as burdocks. Others, 

 producing at their edge a row of brilliantly colored and attractive 

 florets, which serve the purpose of petals for the compound head, 

 branched off into all the marvelous wealth of daisies, asters, sunflow- 

 ers, marigolds, dahlias, golden-rods, ox-eyes, and cinerarias. In yet 

 others the whole mass of the florets, central as well as external, has 

 assumed this ray-like or strap-like form ; and to this group belong the 

 dandelions, hawk-weeds, salsifies, lettuces, sow-thistles, chiccories, nip- 

 pleworts, and cat's-ears. By far the most successful of all flowering 

 plants, the composites have taken possession in one form or another of 

 the whole world ; and among the entire wealth of their extraordinary 

 diversity there is no group more universally fortunate than the com- 

 mon thistle. "What from the purely agricultural point of view we 

 describe as a very persistent and almost ineradicable weed, from the 

 higher biological point of view we should more properly regard as a 

 dominant and admirably adapted species of plant. The one conception 

 is merely narrow, practical, and human ; the other is positive, philo- 

 sophical, and universal. — Longmans' Magazine. 



