308 
Index to Recent Literature Relating to American Botany, 
Abnormal Water-Pore. (Bot. Gaz. xvi. 235, illustrated). 
Description ofa peculiar water-pore found in a leaf of 7vope- 
olum mazus. 
Against the Using of Revertible Generic Names. Edward L. 
Greene. (Pittonia, ii. 185-195). 
Professor Greene comes out squarely in support of the princi- 
ple that a name once used is applicable only to the species or 
genus to which it was originally applied and not to any other. 
The following genera are taken up: Xy/othermia in place of 
Pickeringia, Nutt. (1840) of the Leguminosz, not Nuttall (1834) 
of the Myrsinez, now referred to Ardisia ; Osmarontia in place 
of Nuttallia, T. & G. (1840) of the Rosacez, not Raf. (1818), nor 
DC. (1821), nor Barton (1823); Chrysamphora in place of 
Darlingtonia, Torr. (1853) of the Sarraceniaceze, not DC. (1825) 
of the Leguminose ; L/gopsis in place of Crantzia, Nutt. (1818), 
not Scop. (1777), nor Swartz. (1788), nor Schreb. (1789); Memo- 
serts in place of Rafinesquia, Nutt. (1841), not of Raf. (1838) ; 
Tumion, Raf. (1840) in place of Zorreya, Arnott (1838), not of 
Raf. (1818 and 1819), nor of Spreng. (1821), nor of Eaton (1833). 
Antiquity of the Last Glacial Period—The. N. S. Shaler. 
(Proc. Bost. Soc. Nat. Hist. xxv. 258-267). 
The author utilizes the computed average rate of diffusion of 
tree life to calculate the probable time that elapsed since our 
hickory and walnut treescould have advanced from the southern- 
most extremity of the great ice sheet to where we now find them. 
It is assumed that they have advanced on an average over a belt 
about 400 miles in width, northward from the ancient ice front, 
and it is calculated, from data available at the present time, that 
each generation of trees (occupying a period of thirty years) ad- 
vances about 200 feet by the natural dissemination of the seeds. 
On this basis it would take 300,000 years to traverse the 400 
miles. 
This result evidently startled the author and he hastens to 
say that it is evident the period is altogether excessive, and ac- 
counts for the necessary abbreviation of time by the more speedy 
carriage of seeds by rodents, tornadoes and primitive races of 
men, In conclusion he says: “ Making allowance for the action 
