224 



KNOWLEDGE. 



[October 1, 189G. 



■went on, with some short pauses, until the level of 

 the waters ultimately reached eighty feet below the 

 present surface at the mouth of the Niagara (lorge, 

 when the Niagara River was about four miles longer than 

 now. 



The Niagara River, which had first been a strait joining 

 Lake I'a-ie to the Ontarian (lulf, became a wide, shallow, 

 rapid stream; and then, as the waters of the lower lake 

 subsided, its bed narrowed and its fall iueroased to four 

 hundred and twenty feet. ]'>ut the river was soon greatly 

 enlarged. 'I'he hind was rising to the north of Ontario as 

 well, and ultimately the outlet from Ijake Huron to the 

 Ottawa ^"allcy was blocked, and the surplus waters of the 

 three greatest lakes llowed by their present course to Lake 

 Erie, and thence by the Niagara River. 



With the continued rise of the laud, especially towards 

 the east of Ontario, the water-level rose until it attained 

 its present elevation, and the fall of the river between the 

 two lakes was reduced to the present three hundred and 

 twenty-six feet. 



Can dates be assigned to these events '? The first 

 estimate of the age of Niagara River was given by Ellicott 

 over a century ago at fifty-five thousand four hundred 

 and forty years ; Hakewell, in 1830, gave twelve 

 thousand ; Ijyell's estimate of thirty-five thousand was 

 accepted for many years after 1841 ; but recent writers, 

 using the mean rate of recession during forty-eight years 

 as determined by surveys, make the value about nine 

 thousand years. 



] >r. Spencer has made a new and careful computation of 

 the age of the Niagara River and Falls. He shows that the 

 recent estimates have not taken into account the various 

 changes that liave occurred in the fall and volume of the 

 river. His calculations result in a value nearly that of 

 Lyell's. Dr. Spencer believes the Niagara River was 

 formed thirty-two thousand years ago, and that a thousand 

 years later the falls were in existence. For seventeen 

 thousand two hundred years their height was about two 

 hundred feet ; thereafter the water fell four hundred and 

 twenty feet. Seven thousand eight hundred years ago 

 the drainage of Lakes Superior, Michigan, and Huron first 

 flowed through the Niagara Gorge, and three thousand 

 years ago the waters rose in Lake Ontario until the level 

 reached that of to-day. The falls, then, are thirty-one 

 thousand years old. This estimate, calculated from the 

 rate of erosion, is confirmed by another made from the 

 terrestrial movements. 



Two deductions may be given — one as to the past, the 

 other concerning the future. 



The lakes came into existence after the glacial epoch, 

 and Niagara after the lakes ; and calculations based on the 

 mean rate of rise of the beaches in the earlier period of 

 the lakes' history show " that the close of the ice age 

 may safely be placed at fifty thousand years ago." 



As to the future. " With the present rate of calculated 

 terrestrial uplift in the Niagara district, and the rate of 

 recession of the falls continued or even doubled, before the 

 cataract shall have reached the Devonian escarpment at 

 Bufi'alo, that limestone barrier shall have been raised so 

 high as to turn the waters of the upper lakes into the 

 Mississippi drainage by way of Chicago. An elevation of 

 sixty feet at the outlet of Lake Erie would bring the rocky 

 floor of the channel as high as the Chicago divide, and an 

 elevation of seventy feet would completely divert the 

 drainage. This would require five thousand to six thousand 

 years at the estimated rate of terrestrial elevation." 

 ♦ 



"A Ceocodile Mtjsimy." — Tlie reference to the reign of Ptolemy 

 PliOadelplius as ii.c. 330, at page 211 of the September Number, 

 slioiild have read " B.C. 2H()," 



THE TRANSITION FROM STEM TO ROOT. 



By A. Maslen. 



WHILST all students of botany may be presumed 

 to be sufficiently acquainted with the minuter 

 structure of the Phanerogamic members, and 

 to know the fundamental anatomical dis- 

 tinctions between the stem and its direct 

 prolongation downwards, the root, there still exists a 

 region, viz., the hypocotyl — in which the actual transition 

 takes place — about which their knowledge is perfectly nil. 

 For information on this particular the student may search 

 in vain in the ordinary smaller botanical text-books, 

 excepting only the admirable little book of Dr. Scott 

 ("Structural 13otany." London: Adam & Charles Black, 

 1894), in which will be found a very clear though 

 necessarily short account of the transition as it takes place 

 in the Wallflower. 



It seems opportune, therefore, now that a considerable 

 amount of work has been done on this neglected subject, 

 although very much still remains to be done, to endeavour 

 to give a necessarily short but succinct account of our 

 present knowledge. 



It may, perhaps, conduce to clearness if we give just a 

 brief rrsunu'' of the structure of a stem and root of a 

 typical Dicotyledon or Gymnosperm. In a transverse 

 section of such a stem we see around the pith an inter- 

 rupted zone of vascular bundles, each of which consists 

 of phloem lying externally, i.e., next the cortex, folloTved 

 inwards by the xylem or wood, between which and the 

 phloem is a band of actively dividing cells— the cambium. 

 Such an arrangement, in which the xylem and phloem 

 groups both lie on one and the same radius, constitutes 

 what is known as a collateral bundle. But a point of 

 great anatomical importance has been omitted, namely. 



TrrB I. — A, Diagram showing longitudinal course of bundles 

 through hypoeotvl. P The phloem. X The xylem (smiller elements 

 the proto-x_\lem ) B, C, D, E, Diagrammatic tr.insverse sections 

 through the hypocotyl showing transition from stem to root structure, 

 r The phloem", p x The proto-xylem. B, Through fg. C, Through 

 n I. D, Through K L. K, Root structure. (The arrows indicate the 

 way ia which the rotation of the proto-xyleui takes place). 



that in the stem the first-formed xylem, or proto-xylem, 

 which consists of smaller elements than either the later- 

 formed primary xylem or the secondary xylem formed by 

 the activity of the cambium, and which, moreover, is the 

 only part of the xylem having annular or spiral thickening, 

 (V aliiiii/n internal, i.e., 7ie.rt iha pith. 



If, now, we turn to the root, diflferences are at once 

 evident. If we examine a sufficiently young root (before 

 secondary thickening has set in) we shall see that each 

 bundle consists not of xylem and phloem, but of only one 

 of these constituents, and that, moreover, the xylem does 



