ENTOMOLOGIST AND BOTANIST. 



279 



structiou of vegetation which attended the 

 glacial period, during which the surface was 

 plowed up by glaciers, and afterward exposed 

 to the commotion of the sea, which overspread 

 the laud, burying evei-ything in promiscuous 

 ruin ; but yet by this very means storing away 

 the seeds which, when brought to the surface 

 after the lapse of a geological age, are possessed 

 of vitality and able to reclothc the barren earth 

 with verdure and beauty ! AVho can say that 

 this prolonged vitality of seeds is impossible ? 

 Who can say that it possesses the slightest degree 

 of prohahiliiy ? 



Most cordially do we assent to the following 

 observations of Prof. W: "It must be confessed 

 that the crucial observation is yet to be made. 

 If vegetable germs exist in the drift they can be 

 discovered beforehand ; and until they have been 

 actually detected, it is probable that even the 

 convincing facts cited above will fail to secure 

 universal assent to our proposition involving 

 the prolonged vitality of the seeds of preglacial 

 vegetation." It is the misfortune of science 

 that too many plausible theories have been 

 promulgated without first obtaining the crucial 

 experiment. 



We pass to the consideration of the fifth prop- 

 osition : "In proportion as the diluvial surface 

 became exposed, the flora of the preglacial epoch 

 was reproduced." We may readily believe this 

 to have been the case, if the fact be established 

 that " the diluvial deposits were everywhere 

 replete with living germs." 



It will be observed that this proposition ap- 

 plies, not to the prairie region, but to the older 

 poriious of the continent. The former became 

 "avast inland sea, upon whose bottom gathered 

 the lifeless sediments that were to be the soil of 

 the prairies." When this surface was finally 

 drained, it was left "a naked and lifeless expanse 

 of vegetable slime," containing no vegetable 

 germs, and by its nature preventing the develop- 

 ment of any, in the diluvial matter below. 



But we hasten to the consideration of the 

 final proposition — "The vegetation which finally 

 appeared on the drained lacustrine areas was 

 extra-limital, and was more likely to be herba- 

 ceous than arboreal." The substance of this 

 proposition seems to be that the vegetation 

 which first clothed the prairie region was intro- 

 duced from beyond its limits, by the three 

 natural agencies of winds, running water and 

 animals; and that because the seeds of trees, as 

 the oak, hickory and walnut, were heavier than 

 the seeds of grasses and herbs, they were not so 

 easily dispersed, and therefore the prairie became 

 covered with herbaceous vegetation exclusively. 



We do not see that in this proposition any use 

 has been made of the theory which has been so 

 extensively elaborated by Prof. W., unless it be 

 to account for the occurrence of that extra- 

 limital vegetation which formed " a shining 

 ridge of forest trees around the margins of the 

 prairies." AVhere were these margins ? The 

 ancient lake, which finally became the prairie 

 region, reached its arms into Iowa, and into 

 northern Indiana and southwestern Michigan. 

 The margins of this lake, then, were in Iowa on 

 the west, and in Indiana and Michigan on the 

 northeast. The northern and southern bound- 

 aries are not directly given, but we may reason- 

 ably suppose them to have been as widely 

 separated as those of the west and east. Here, 

 then, was a "naked and lifeless expanse of 

 vegetable slime." 



Is this meant for a picture of a lake region 

 rapidly drained ? If rapidly drained, a large 

 portion of the lacustrine sediment would have 

 been washed away, exposing, in thousands of 

 places, the diluvial deposits; the living germs 

 with which they were replete would then have 

 been exposed to the genial influences of sun and 

 air, and would have reproduced the ancient 

 vegetation. But no — the vegetation of the 

 prairie region was "extra-limital," and brought 

 in by the agency chiefly "of winds, animals and 

 running waters." We have great faith in these 

 agencies, and believe they are sufficient to ac- 

 count in great measure for the vegetation, not 

 only of the prairie region, but of the continent. 

 In the prairie region the forests principally 

 form belts around the large water-courses. These 

 drainage channels furnished favorable localities 

 for the growth of certain kinds of trees, particu- 

 larly the Willows and Cottonwoods. These 

 may be called the pioneers of the forest ; their 

 seeds are light, and covered with a cottony 

 down, which causes them to be easily carried 

 before the winds for great distances. They 

 would naturally find lodgment and development 

 in advance of many other forest trees with 

 heavier seeds. But having established a line of 

 trees, or of scattered groves, on the margin of a 

 stream, they would be constantly visited by 

 birds and animals, which would gradually in- 

 troduce the seeds of other forest growths, and 

 thus the boundaries of the forest would be ex- 

 tended. The fruit of the wild cherry and plum, 

 the mulberry, hackberry. black gum, and many 

 other trees, are eagerly eaten by birds, and the 

 pits are voided uninjured for purposes of vege- 

 tation. 



As the veins of a leaf all converge from the 

 circumference to a common point, so the lines 



