Destruction 

 Development 



SCIENTIFIC SIDE-LIGHTS 



164 



of man, and on the scale of his observation, 

 carries in it, to the myriads which people 

 this little leaf, an event as terrible and as 

 decisive as the destruction of a world. Now, 

 on the grand scale of the universe, we, the 

 occupiers of this ball, which performs its 

 little round among the suns and the systems 

 that astronomy has unfolded we may feel 

 the same littleness, and the same insecurity. 

 We differ from the leaf only in this circum- 

 stance, that it would require the operation 

 of greater elements to destroy us. But these 

 elements exist. CHALMERS Astronomical 

 Discourses, p. 37. (R. Ct., 1848.) 



800. DESTRUCTION OF TREES 

 CHANGES EARTH'S SURFACE When 

 traveling in Georgia, in 1846, I saw the com- 

 mencement of hundreds of valleys in places 

 where the native forest had recently been re- 

 moved. One of these newly formed gullies 

 or ravines . . . occurs on the road to 

 Macon. Twenty years ago, before the land 

 was cleared, it had no existence; but when 

 the trees of the forest were cut down, cracks 

 three feet deep were caused by the sun's 

 heat in the clay; and, during the rains, a 

 sudden rush of water through the principal 

 crack deepened it at its lower extremity, 

 from whence the excavating power worked 

 backwards, till, in the course of twenty 

 years, a chasm, measuring no less than 55 

 feet in depth, 300 yards in length, and vary- 

 ing in width from 20 to 180 feet, was the 

 result. The highroad has been several 

 times turned to avoid this cavity, the en- 

 largement of which is still proceeding, and 

 the old line of road may be seen to have held 

 its course directly over what is now the 

 wildest part of the ravine. LYELL Prin- 

 ciples of Geology, ch. 14, p. 204. (A., 1854.) 



801. DESTRUCTION, VIEWLESS 

 AGENT OF Frost Disintegrates Rocks and 

 Breaks Down Mountains. The disintegra- 

 ting action of rain in temperate and high 

 latitudes is greatly aided by frost, and the 

 same is the case in the elevated tracts of more 

 southern latitudes. Rain renders the super- 

 ficial portions of rock more porous, and thus 

 enables frost to act more effectually; while 

 frost, by widening pores and fissures, af- 

 fords readier ingress to meteoric water. 

 . . . The great heaps or " screes " of 

 rock-rubbish which cloak the summits and 

 slopes of our mountains, and gather thickly 

 along the base of precipice and cliff, have 

 been dislodged by frost and rolled down from 

 above, their progress downward being often 

 aided by torrential rains, melting snow, and 

 the alternate freezing and thawing of the 

 saturated debris itself. GEIKIE Earth 

 Sculpture, ch. 2, p. 28. (G. P. P., 1898.) 



802. DEVELOPMENT DELAYED FOR 

 A PURPOSE Device to Secure Cross-fertili- 

 sation. In Spiranthes the young flowers, 

 which have their pollinia in the best state 

 for removal, cannot possibly be fertilized; 

 they must remain in a virgin condition un- 



til they are a little older and the column 

 has moved away from the labellum. Here 

 the same end is gained by widely different 

 means. The stigmas of the older flowers are 

 more adhesive than those of the younger 

 flowers. These latter have their pollinia ready 

 for removal; but immediately after the ros- 

 tellum has exploded it curls forwards and 

 downwards, thus protecting the stigma for 

 a time; but it slowly becomes straight 

 again, and now the mature stigma is left 

 freely exposed, ready to be fertilized [by 

 pollen from another flower]. DARWIN Fer- 

 tilization of Orchids, ch. 4, p. 121. (A., 

 1898.) 



803. DEVELOPMENT FROM THE 

 CELL Embryos of a Sheep, Tiger, Lizard, 

 Bird, and Ape Indistinguishable Each Ani- 

 mal Recapitulates the History of Its Race. 

 Every animal or plant begins its existence 

 as a cell, which develops by a process of re- 

 peated fission and growth into the perfect 

 form. But if we trace the different types 

 backward, we find that we come to a stage 

 when the embryos of all the members of an 

 order, such as the various species of rumi- 

 nants, are indistinguishable; earlier still 

 all the members of a class, such as the mam- 

 malia, are equally alike, so that the em- 

 bryos of a sheep and a tiger would be al- 

 most identical; earlier still all vertebrates, 

 a lizard, a bird, and a monkey, are equally 

 indistinguishable. Thus in its progress 

 from the cell to the perfect form every ani- 

 mal recapitulates, as it were, the lower 

 forms upon its line of descent, thus afford- 

 ing one of the strongest indirect proofs of 

 the theory of evolution. The earliest defi- 

 nite result of cell-division is to form what is 

 termed the " gastrula," which is a sac with 

 a narrow mouth, formed of two layers of 

 cells. All the higher animals, without ex- 

 ception, from mollusk to man, go through 

 this " gastrula " stage, which again indi- 

 cates that all are descended from a common 

 ancestral form of this general type. WAL- 

 LACE The Wonderful Century, ch. 14, p. 144. 

 (D. M. &Co., 1899.) 



804. DEVELOPMENT, GRADUAL 



Of Arts and Sciences Antiquity of Egyp- 

 tian and Babylonian Culture. On the whole 

 it appears that wherever there are found 

 elaborate arts, abstruse knowledge, complex 

 institutions, these are results of gradual de- 

 velopment from an earlier, simpler, and 

 ruder state of life. No stage of civilization 

 comes into existence spontaneously, but 

 grows- or is developed out of the stage before 

 it. This is the great principle which every 

 scholar must lay firm hold of, if he intends 

 to understand either the world he lives in 

 or the history of the past. Let us now see 

 how this bears on the antiquity and early 

 condition of mankind. The monuments of 

 Egypt and Babylonia show that toward 

 5,000 years ago certain nations had already 

 come to an advanced state of culture. No 

 doubt the greater part of the earth was then 



