92 Correspondence — Rev. Professor S. Haughton. 



My contention, in brief, was this, that the Tertiary plant-remains 

 indicating a climate similar to that of Lombardy (so far as heat is 

 concerned) are so situated round the North Pole that no possible 

 change in the position of that Pole (even were such permitted by 

 mechanical considerations) would give them the climatic conditions 

 as to temperature which they require. It was urged at the meeting, 

 as an objection to my view, that the presence of evergreens among 

 the Arctic Tertiary plants was inconsistent with the prolonged 

 absence of light, which they must have sustained if the Pole were in 

 its present position. To this, my reply was the following statement 

 by Professor W. E. McNab, M.D., of the Koyal College of Science : — 

 " 4, Vernon Parade, Clontarf, 1th April, 1878. 



" Dear Dr. Haughton, — I fear I cannot give you a direct answer to your 

 question, and I have not found any papers on the subject in the ' Botanischer 

 Jahrsbericht,' Sachs' ' Lehrbuch der Botanik,' in Sachs' ' Handbuch der Experi- 

 mental- Physiologie der Pflanzen.' The general facts of the case can, however, be 

 very readily stated. 



" Plants containing green chlorophyll grains, when placed in darkness, partial or 

 complete, change colour from the destruction of the chlorophyll. Sachs says (Text- 

 book of Botany, page 669) that in the leaves of rapidly-growing Angiosperms the 

 absorption and disappearance of the chlorophyll takes place in a few days if the 

 temperature be high. He adds, Cactus stems with slow growth, and the shoots of 

 Selaginella, remain green for months in the dark. It is probably true also of 

 Conifers, as I have seen them kept in the dark during the winter months without 

 injury. This I saw in Berlin. Large plants requiring protection from the cold were 

 laid on their sides, and a covering of mats and leaves on a wooden frame placed 

 over them. 



" The evergreens in your list are all Conifers, and I am of opinion that the 

 absence of light for a considerable period would not injure them. 



" It is well known that cold alters the colour of the leaves of many Conifers at 

 once, but in your paper you state the temperature at 48° F., a temperature much too 

 high to influence the colour. 



" Your question places an isolated physiological fact in a very important light, at 

 least it appears to do so to me. I give it in Sachs' words (Text-book, page 665) : 

 * If the temperature is sufficiently high, the green colouring substance is found in 

 the cotyledons of Conifers and in the leaves of Ferns, in complete darkness as well as 

 under the influence of light. . . . Provided,' therefore, that the temperature is 

 favourable, the chlorophyll in the cotyledons of Conifers and the leaves of Ferns does 

 not require light in order to assume its green colour, while that in Angiosperms does 

 require it, and in both cases the change does not take place at low temperature.' 



" My answer to the objection that has been made to your paper is this : ' Grant 

 that the evergreens cannot stand prolonged absence of light — that refers to Angio- 

 spermous forms. Here all the forms are Coniferous; and Coniferous plants with 

 Ferns have the peculiar property of forming green chlorophyll grains in the dark.' 



" I think a few evergreens do stand prolonged darkness, as I have certainly seen 

 myrtles and rhododendrons placed during the winter in very dark sheds. 



" As I can only refer to the books in my own library to-day, I shall try to find out 

 some reference to the St. Petersburg observations, and let you know the result in 

 due course. — I am, very truly yours, 



(Signed) W. E. McNab." 



" Eev. Prof. Haughton, F.E.S., etc., etc." 



During the discussion on my paper in the Geological Section, it 

 was observed by Mr. Pengelly that " magnolias'' are mentioned by 

 Professor Heer as occurring among the Greenland Tertiary plants. 

 To this my reply was, that although some of the magnolias are ever- 

 greens, some of them also have deciduous leaves, and that the 

 occurrence of plants or trees having deciduous leaves should cause us 



