Maech 6, 1914] 



SCIENCE 



357 



Dr. Ludwig Diels, of Marburg, has been 

 appointed associate professor of botany in the 

 University of Berlin, and assistant director 

 of the Botanical Garden and Museum. 



DISCUSSION AND COBBESPONDENCE 



FOSSIL PLANTS IN THE PANAMA CANAL ZONE 



Except for the incidental mention by 

 Pilsbry and Brown of lignified nuts in their 

 paper on the MoUusca I know of no record of 

 any remains of fossil plants having been 

 found in the Canal Zone, notwithstanding the 

 fact that the numerous Tertiary tufEs would 

 seem to furnish an admirable matrix for the 

 preservation of leaf impressions. 



During 1912 Dr. M. I. Goldman, of the 

 Johns Hopkins University, visited the Isthmus 

 and in connection with his work on rock 

 weathering devoted considerable time to a 

 search for fossil plants along the Canal with 

 the results indicated by the following note. 



Since fossil plants of Tertiary age from the 

 tropics have not been collected or studied to 

 any large extent and since the Tertiary floras 

 of Central America have a most important 

 bearing on both the phytologic and geologic 

 history of southeastern North America during 

 the Tertiary, a preliminary announcement 

 seems justifiable. 



Fossil plants seem to be somewhat sparsely 

 but widely distributed along the canal and 

 identifiable forms were collected from the fol- 

 lowing localitites: 



1. East wall of the Culebra Cut just north 

 of station 1760 and opposite Culebra. 



2. West wall of cut below Miraflores locks, 

 where the plant-bearing tuff outcrops for about 

 one fourth of a mile. 



3. Culebra Cut under the steep hill just 

 north of Paraiso, associated with specimens of 

 the pelecypodian genus Phacoides. 



4. Gatun Dam borrow pits. 



The best material comes from the first of 

 these localities and the least satisfactory from 

 the last. The collections have not been criti- 

 cally studied, since it is hoped that more ex- 

 tensive collections will be sent in by the resi- 

 dent geologist of the Canal Commission. 



The following forma have been recognized 



in a preliminary study of the collection: A 

 fine large species of Guatieria which is present 

 at several localities; a well-marked species of 

 Myrtacese, probably representing the genus 

 Calyptranthes; a species of Neciandra; a 

 species of Ehamnacece; a characteristic small- 

 leaved species of Ficus; another of Ocotea; a 

 species of Eubiacew and one of Melastomacece. 

 Petrified wood was also collected and although 

 but three slides have been cut these show ap- 

 parent identity with a species described from 

 the Oligocene of the Island of Antigua. 



None of the material lends any support to 

 the view, at one time prevalent, that some of 

 the Isthmian beds represent deposits of Eocene 

 age, and while the various plant-bearing beds 

 are probably not exactly synchronous, their 

 floras in so far as they are known from the 

 present small collection all appear to be refer- 

 able to the Oligocene. 



Edward W. Beert 



Johns Hopkins University, 

 Baltimoke, Md. 



WHAT grades represent 



The following considerations have been of 

 service to the writer in the diagnosis of the 

 difiieulties encountered by students in meeting 

 the scholastic requirements represented by 

 grades, and the identifying of the obstacles 

 has often assisted in their removal. 



It is not necessary in this discussion to 

 assume any more definite or uniform system 

 of grading than that 100 per cent, represents a 

 perfect grade and that there is a minimum 

 grade required to entitle the student to credit 

 for the course. Half way between these is 

 what may be called an average grade. This 

 does not mean the grade that a class would 

 average under the usual conditions, but what 

 a class might be expected to average if all 

 members gave all the officially allotted time 

 (or a reasonable time) and their best effort to 

 the subject — quite a different matter ! The 

 instructor should make his demands such that 

 the student of average qualifications using his 

 best effort all the allotted time would receive 

 the average grade — half way between the pass- 

 ing grade and 100 per cent. 



