THE SCOPE OF BOTANY. 665 



to the southward or to perish. The Isthmus of Panama and the 

 broad expanse of Central America offered a refuge for the tender 

 forms which could not withstand the rigors of the Ice Age when 

 North America was covered to the Ohio Valley with a great con- 

 tinental glacier. In the milder climes many of them survived, 

 and as the ice retreated they slowly followed it how, I shall take 

 occasion to show in a moment. But between the ice-bound con- 

 tinent of Europe and the warmer lands to the southward inter- 

 vened then as now the broad expanse of the Mediterranean, which 

 could be traversed but by few animals and by still fewer plants. 

 Many forms perished, and their places are empty to this day. 

 Hence we see one reason for the greater number of plant species 

 on our own continent. 



The botanical geologist finds other things to study, for there 

 are many plants of bygone ages preserved to this day as fossils in 

 the rocks of various horizons. The science of paleobotany grows 

 more slowly than the science of paleozoology, which greedily 

 usurps the name of paleontology, as if plants were not quite as 

 important, had not contributed quite as much of value to the 

 earth's crust, as animals. The reasons why paleobotany is such a 

 slow- growing and fragmentary science are two. In the first place, 

 as I have suggested, paleontologists devote themselves in their 

 investigations and teaching too exclusively to animal remains, 

 and hence he who will know more of the plants of past ages must 

 study and learn largely unaided. But the second reason is more 

 fundamental namely, that plant structures are less easily pre- 

 served than those of animals (whose shells or other hard parts 

 are very resistant), and hence many have been destroyed during 

 the various changes that the rocks in which their remains were 

 imbedded have undergone. The fossil remains which are now 

 known give confirmation of the fact mentioned a moment ago that 

 plants are ever changing. The plants of the Carboniferous Age 

 were very different from those of to-day. The aspect of field and 

 forest then must have been mysterious indeed ; the heavy atmos- 

 phere, the intense light, the moisture, contributing to a vegetation 

 of more than tropical luxuriance. Between the lofty stems of 

 tree ferns, in the deep shade cast by their great fronds, wandered 

 animals hideous to the eye, though perhaps no more dangerous 

 than our mild-eyed cows. But we find to-day, growing here and 

 there, plants which greatly resemble those of the coal measures, 

 not only the ferns, but the horsetails (scouring rushes of our an- 

 cestors, Equisetum), the Lycopodiums, without which no northern 

 Christmas festival is quite complete, and others less conspicuous. 

 These the paleontologist convinces us are the direct descendants 

 of those plants which compose our coal. He thereby adds his 

 facts to that history of life which shows that plants are related, 



