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THE POPULAR SCIENCE MONTHLY. 



side of their bases of support, which protect 

 them from the intrusion of the heavier par- 

 ticles. For that reason perpendicular and 

 water-logged or floating timbers, submerged 

 stumps of trees, and branches drooping into 

 the water from trees or bushes along the 

 banks, are favorite locations. They do not 

 disdain more temporary support, such as 

 weeds and water-grasses. . . . Through the 

 clear water of our Northern lakes we may 

 often see them lying in slender lines upon 

 the leaves of submerged weeds, or in beauti- 

 ful, cushion-like masses upon the stones or 

 gravel." The best season for collecting them 

 is from July till late in November. 



Geological Floras. — M. de Saporta's 

 views on the origin of our forest-groupings 

 were substantially concurred in by Prof. W. 

 Boyd Dawkins, in his vice-presidential ad- 

 dress before the Geological Section of the 

 British Association. Having referred to the 

 characteristic features of the earher floras, 

 much as M. de Saporta has done, and to the 

 antiquity of the gingko (which has descend- 

 ed from the Carboniferous age), he says: 

 " In North America the flora of the Dakota 

 series so closely resembles the Miocene of 

 Switzerland that Dr. Heer had no hesitation 

 in assigning it in the first instance to the Mio- 

 cene age. It consists of about one hundred 

 species, of which about one half are close- 

 ly allied to those now living in the forests 

 of North America — sassafras, tulip, plane, 

 willow, oak, poplar, maple, birch, together 

 with sequoia, the ancestor of the giant red- 

 wood of California. The first palms appear 

 also in both continents at this place in the 

 geological record. In the Tertiary period 

 there is an unbroken sequence in the floras, 

 as Mr. Starkie Gairdner has proved, when 

 they are traced over many latitudes, and 

 most of the types still survive at the present 

 day, but slightly altered. If, however. Ter- 

 tiary floras of difi^erent ages are met with in 

 one area, considerable differences are to be 

 seen, due to progressive alterations in the 

 climate and altered distribution of the land. 

 As the temperature of the northern hemi- 

 sphere became lowered, the tropical forests 

 were pushed nearer and nearer to the equa- 

 tor, and were replaced by plants of colder 

 habits from the northern regions, until, in 

 the Pleistocene age, the arctic plants were 



forced far to the south of their present habi- 

 tat. In consequence of this, Mr. Gairdner 

 concludes that ' it is useless to seek in the 

 arctic regions for Eocene floras as we know 

 them in our latitudes, for during the Tertiary 

 period the climatic condition of the earth did 

 not permit their growth there. Arctic fossil 

 floras of temperate and, therefore, Miocene 

 aspect are in all probability of Eocene age, 

 and what has been recognized in them as a 

 newer or Miocene fades is due to their hav- 

 ing been first studied in Europe in latitudes 

 which only became fit for them in Miocene 

 times. "When stratigraphical evidence is 

 absent or inconclusive, this unexpected per- 

 sistence of plant-types or species throughout 

 the Tertiaries should be remembered, and the 

 degrees of latitude in which they are found 

 should be well considered before conclusions 

 are published respecting their relative age.' 

 This view is consistent with that held by the 

 leaders in botany — Hooker, Dyer, Saporta, 

 Dawson, and Asa Gray — that the north polar 

 region is the center of dispersal, from which 

 the dicotyledons spread over the northern 

 hemisphere." 



Science and Trade-Rontes. — In the first 

 part of his presidential address before the 

 Geographical Section of the British Associa- 

 tion, Colonel Sir C. W. Wilson showed, by nu- 

 merous historical references, how the trade- 

 routes of the world are and have always been 

 governed by physiographical conditions, and 

 by accidents of war and human operations, 

 which, making one route inconvenient, have 

 compelled the opening of another. To cope 

 with these conditions, and find and possess 

 the best route, is one of the functions of the 

 scientific geographer. The discovery of the 

 Cape route was no mere accident, but the 

 result of scientific training, deep study, care- 

 ful preparation, and indomitable persever- 

 ance. Prince Henry, having determined to 

 find a direct route to India, invited the most 

 eminent men of science to instruct a number 

 of young men who were educated under his 

 own eye, and in a few years he made the 

 Portuguese the most scientific navigators ia 

 Europe. The voyage of Vasco da Gama, with 

 its grand commercial results, followed. For 

 a correct determination of the lines which 

 the shortened trade-routes and great mari- 

 time canals we are seeking to locate should 



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