64 



GARDENERS' CHRONICLE 



Disappearing Species 



WILLARD N. CLUTE 



H(J\VEVER much eminent lecturers and Southern 

 politicians may disagree with the evolutionists 

 as to how the plants and animals came upon the 

 earth, they are not likely to differ much over the state- 

 ment that many species are gradually disappearing. 

 The evidence is all too conclusive. In very recent 

 times we have seen the passenger pigeon, and the 

 quagga, the sea-cow, great auk. exterminated and the 

 buffalo, whale, prairie-hen and many kinds of birds 

 brought to the verge of extinction. That a large 

 number of others are also on the way out can scarcely 

 be doubted. As regards the cases mentioned, it may 

 be objected that these are not due to natural causes 

 but are mainly due to the activities of man. Granting 

 this, the proposition is still the reaction of one species 

 upon another. The results in the end are the same, 

 whether the struggle is between plant and animal, 

 between plant and plant, or between the animals ana 

 that most destructi\-e animal of them all — man. 



It is likely that a thousand small adjustments are 

 constantly taking place in fitting plants and animals 

 more exactly to their surroundings. It is only when 

 the adjustments are too slow to preserve the life of 

 the species, or when they are more rapid than usual, 

 that we notice them. In the case of the passenger 

 pigeon, extermination was unusually rapid. It occurred 

 in the span of a single lifetime. The death of the 

 chestnut trees has been still more rapid. Twenty 

 years ago, our eastern mountains contained numerous 

 magnificent forests of chestnut. Now the tree is prac- 

 tically extinct; killed by a microscopic enemy in spite 

 of the best efforts of man to protect it. 



The fossil record is chiefly a record of species that 

 no longer inhabit the earth; of unsuccessful species 

 that failed to keep up with the changes in their sur- 

 roundings. The plants that formed the coal measures 

 are not represented on the earth today. Indeed, the 

 existence of fossil palms in Greenland and the occur- 

 rence of coal beds in regions now covered with snow 

 and ice show very conclusively that great changes 

 must have taken place since the coal plants flourished. 

 In other regions we may find species that have not 

 entirely disappeared, but whose restricted ranges show 

 how greatly their race has declined. The magnolias 

 of our Southern States and Eastern Asia were once 

 common in Eurojje as shown by their fossil remains, 

 but they do not grow there now. The redwoods now 

 found only along our Pacific Slope were once spread 

 entirely around the earth in the north tem])erate zone. 

 When we a.sk what brought these species low there 

 is no definite answer. Perhaps it was a change in climate, 

 j)erhaps too great a difference in teiriperature, or moistiire, 

 or some other condition of which we are ignorant at 

 present. 



Probably few of us realize how very dcpendenl even 

 man himself is on the conditions of his environment. 

 Any one of a dozen slight changes that might take 

 place in the earth's atmosphere would instantly wijie 

 him out of existence. A succession of years ton cold 

 for the growing of food crops would force liim inward 

 the equator just as an increase of warmth would in- 

 duce him to move nearer the poles. The remains of 

 once ]K>pulous cities in the deserts of .\sia and the 

 abandoned cliff-ruins so widely scattered in our arid 

 Southwest point mutely to the fact that nmisturc con- 



ditions on the earth have changed greatly since man 

 made his appearance. That he coulcf not stand against 

 some of these changes is shown by the successive 

 waves of migration that have flowed into Europe from 

 the south-east, dri\-en out by the increasing dessication 

 of the region. 



What man has done to exterminate various species 

 is not worth mentioning in comparison with Nature's 

 eft'orts in the same line. The broad sea that once 

 rolled from the Gulf of Mexico to the Arctic ocean con- 

 tained many species that disappeared with its sub- 

 sidence. At the same time a vast region was thrown 

 open to such land animals and plants as could migrate 

 into it and alter their requirements sufficiently to re- 

 tain their place in it. Changes of similar kind have 

 happened again and again over the earth ; indeed, they 

 have not yet ceased to happen. W'hen the changes 

 have been small, or have taken place very gradually, 

 plants and animals have probably changed fast enough 

 to keep pace with them. But when the changes have 

 haj)pened to be rapid, many species have doubtless 

 gone down to defeat, unable to maintain life in a 

 greatly changed environment. 



Nor is the life of a species entirely bound up with 

 its inorganic or physical environment. Often the de- 

 pendence of one species on another, or their mutual 

 reactions may result in the decline and death of one 

 or both. A plant species may disappear for want of 

 the proper pollinating insect, or because of the pres- 

 ence of some leaf-eating insect or other animal. ( )r it 

 may, as in the case of the chestnut, be attacked by 

 some disease that it is unable to survive. Still further, 

 the absence of the pollinating insect may be due to 

 the destruction of some very tlift'erent plant upon 

 which the larval insects feed and this in turn may be 

 due to the drying up of some distant swamp, or the 

 flooding of some valley in which the plant grew. 

 Plants that are incapable of self-pollination may have 

 their very existence threatened in this way. 



Of all the agencies that threaten the existence of 

 plants and animals today, man seems to be the most 

 imjjcjrtant. By lumbering, burning, draining, flood- 

 ing, filling, excavating and cultivating he has greatly 

 changed the face of Nature and rendered many locali- 

 ties entirely imfitted to support the species that 

 formerly inhabited them. But these very changes 

 have made new and fertile fields for still other species 

 that could not get a foothold so long as the original 

 tenants were not disturbed. Mnreover, the cultivated 

 crops that man ])rizes often harbor insects or diseases 

 that spread to the wild forms, while occasionally the 

 tables are turned and the wild things provide diseases 

 that inflict great mortality on the cultivated crops. 

 As a matter of fact, some innocent ap])earing plant 

 may harbor an organism very destructive to a very 

 different species. 



The total result of these inlcracticms ui species with 

 species and of species with climate and the changes 

 in the surface of the earth must be a scries of changes 

 in form and structure which ])rescrves tlu' successful 

 forms from e.xtinction. Thus have the phuits been modi- 

 fied to fit their environment. Thus have resulted ncAv 

 forms which in lime may have become di.siinct species. 

 1 o doubt it is to doubt the evidence of our senses. And 

 this is evolution. 



