January 20, 1905.] 



SCIENCE. 



97 



lem widens, becomes vast as the continent, 

 and any answer that we mal^e must be far- 

 reaching as the flora of a world. 



Our desert lies shining here before us; 

 but not one of these plants except the cac- 

 tus is in broader sense unique ; each has its 

 kin rising in happier fields to fairer for- 

 tune. The yuccas are lilies, but lilies 

 bloom in Bermuda and in Teneriffe, and in 

 every most fertile garden of the world. 

 The mesquite is a Prosopis, but the Prosopis 

 genus shows many a handsome forest tree, 

 and even the mesquite in the Arizona val- 

 leys, where conditions are less hard, rises a 

 forest with trees fifty feet in height. The 

 cactus, as I read it, with undifferentiated 

 floral leaves and abundant sporophylls, is 

 an ancient adaptation to an ancient desert, 

 possibly pre-cretaceous, and takes posses- 

 sion of the world just so fast as the world 

 becomes desert ; unstable in cultivation, not 

 because new, but because reversionary. 



I do not mean to say necessarily that the 

 Alamogordo desert flora has had its origin 

 where it stands, although such a contin- 

 gency is not impossible of thought. Had this 

 been the only desert on the continent its 

 flora is as might have been expected. But 

 there are a hundred similar intra-montane 

 regions whose geologic history is the same. 

 These have in similar fashion originally 

 shaped a flora each for itself. No doubt 

 once similar conditions are set up in re- 

 gions at first unlike, an exchange of species 

 may take place. American cacti are at 

 home in the deserts of Europe and the 

 Russian thistle flourishes on Dakota plains. 



The desert lies shining here before us, 

 changing forever, but all its changes are 

 of imperceptible delicacy and slowness. 

 Its methods would seem not different from 

 those by which nature has from the first 

 essayed the education of the vegetable 

 world. Between salt water and fresh all 

 conditions oft'er by infinitesimal shadings 

 where the rivers meet the sea, thus green 



plants first emerged from ocean; all con- 

 ditions from shore-line low-water mark to 

 dry land, thus the plants at length sat on 

 the shore, wet only by tides or by the gentle 

 rain; all conditions of level by which the 

 plants occupy the kingdom of the upper 

 air: all conditions of spore-union by which 

 they meet at length the problem of aerial 

 fertilization : so that while sports there may 

 be among plants outside the pale of cultiva- 

 tion, nevertheless, they must always be 

 within limits set as result of more gentle 

 changes eft'ected by the slow, and for the 

 most part exquisitely delicate, transforma- 

 tions which make up the history of the 

 planet. Given a desert flora, a cactus flora, 

 for instance, and there may be endless spe- 

 cies-making, by sport, if you will, or other- 

 wise, but in every case a cactus; but the 

 cactus itself is the child of continental 

 movements which brought about some old- 

 time, perhaps cretaceous desert. 



Our desert lies shining before us ; it is old 

 and silent : would you know its secret, read 

 the rocky records that lie behind, around, 

 beneath, and be assured that once the story 

 of yesterday were understood, the facts of 

 to-day would ask no wider explanation. 

 The physical forces of this world still drive 

 the loom that weaves the web of life. Be- 

 fore the loom the unseen weaver sits, guid- 

 ing her web that passes to an endless roll, 

 changing withal the width, the pattern, as 

 conditions rise. Changes her arabesque, it 

 is for cause, changes it not, it is alike for 

 cause ; and if at intervals, as we watch, 

 anon new figures rise, may it not be but the 

 return of some earlier triumphant cycle 

 that here begins anew, evident enough in 

 cause and feature were once that giant 

 scroll unrolled, or were her watchers more 

 patient, more enduring. Alas! in presence 

 of this mighty loom what fleeting, evanes- 

 cent interpreters are we 1 



Thomas H. Macbride. 



