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THE POPULAR SCIENCE MONTHLY, 



ferent plants require different degrees of 

 light and heat for the formation of their 

 colors. Ferns and conifers need but little. 

 Different colors require different degrees for 

 their development ; yellow is an exception, 

 for it seems to be found equally well under 

 the most varied circumstances. Some red 

 flowers, as the tulips, color well in the dark, 

 and the blues and violets seem partly inde- 

 pendent partly dependent on the light. The 

 crocus takes on its deep-blue violet in the 

 dark, while the Prunella grandifiora remains 

 white. A steady supply of nutriment is 

 essential. Askenasy tried some cut branches 

 of foxglove and other plants in a glass ex- 

 posed to a strong light. The first flowers 

 that came out Averc bright, but the others 

 grew paler, and the last were nearly white. 

 The failure of nourishment neutralized the 

 stimulating effect of a strong light. The 

 effect of these external agencies is depend- 

 ent on the disposition of the flower to par- 

 ticular colors. They may aid the tendency, 

 but do not perceptibly modify it. The sup- 

 position that particular seasons are favor- 

 able to the development of particular colors 

 is not fully established ; and the real amount 

 and extent of the influence of changes of 

 season on color is not ascertained. The in- 

 vestigation of the effect of the soil is at- 

 tended with great difficulties. When we 

 change the soil, we change other relations, 

 as those of light and temperature, without 

 being able to measure the part that each 

 may have in producing the result we see. 

 By introducing changes in all the conditions 

 we cause an abrupt modification in the life 

 of the plant, by which it becomes more 

 docile to our treatment. Hence most of 

 the variations take place under cultivation. 

 Variation once started, further changes are 

 comparatively easy. Natural selection oper- 

 ates to perpetuate variations. Those colors 

 which stand out most distinct from the sur- 

 rounding green attract the insects which act 

 as fertilizing agents, and become predomi- 

 nant and permanent. 



A Fortress of the Polished-Stone Age 

 in Sptlint M. A. F. Nogues, mining en- 

 gineer, gives in "La Nature" an account 

 of a fortified camp of the polished-stone 

 age, situated on the plateau of Maestrazgo, 

 Spain, which was discovered by the Abbe 



Ambrosio Sans, and which he has recently 

 visited. The work is situated on the eleva- 

 tion called the Muela de Chert, which con- 

 stitutes the highest groups of hills of the 

 plateau, rising 2,880 feet above the sea. 

 The end of the plateau shows a steep lime- 

 stone ledge inaccessible at almost every 

 point. At a considerable distance from this 

 point, the lines of the fort are marked by 

 an irregularly disposed mass of weather- 

 browned stones running across the ridge 

 which is the continuation of the Muela, and 

 separating the higher parts of the eminence 

 from the lower levels of the plateau. A 

 real fortified inclosure is thus formed, de- 

 fended on one side by the natural precipi- 

 tous escarpment, and by the wall along the 

 rest of the circuit. The curved part of the 

 wall, for a length of about eight hundred 

 feet, is built of stones without mortar, ar- 

 ranged from the level, not of the surface of 

 the ground, but of excavations made in the 

 mountain by the prehistoric builders. On 

 the south, the wall ends at a short distance 

 before reaching the precipice ; and here are 

 found traces of an opening or the gate to 

 the inclosure, which is about eight feet 

 wide at the bottom. In the interior of the 

 fortification are a smaller wall, still intact, 

 and piles of stones, the remains of former 

 habitations, the greater part of which have, 

 however, disappeared. Those which have 

 been traced were of an oval form, about 

 twenty feet long by six and a half feet wide, 

 sometimes grouped, sometimes isolated, but 

 arranged apparently so as to conform to 

 some politic regulation. When the ruins 

 were first discovered, the bones of many 

 animals which are now extinct in Spain, as 

 well as those of some still living in the coun- 

 try, were found at the bottom of the wall. 

 Without the inclosure were found stone im- 

 plements, polished hatchets of a white, red- 

 dish-veined quartz, lance-points of blackish 

 dioritc, and other objects of the polished- 

 stone age. Such a work could only have 

 been constructed by a settled population, 

 who had already attained considerable num- 

 bers. No traditions of the historic period 

 mention such fortifications; and on this 

 fact, as well as on the occurrence of the re- 

 mains of animals that have not lived in 

 Spain for time immemorial, is based the 

 presumption that the structure dates from 



