OCXOBEB 1, 1909] 



SCIENCE 



447 



about it. Stahl, recording that the seedlings 

 of all gymnosperms except Oingko, Wel- 

 wiischia, Cycas and Ephedra are green even 

 when the seeds sprout in the dark, expresses 

 the suspicion that this fact may have phylo- 

 genetic significance. It may; but to the re- 

 viewer such speculations, such suggestions, 

 savoring more of the study than of the labora- 

 tory, are of little use to science. On the 

 other hand, Stahl did not ascertain whether 

 or not there might be difFerences in the 

 amounts of light reaching the developing em- 

 bryos in the ripening seeds of these different 

 classes of gymnosperms. He points out earlier 

 in this paper that the seedlings of maple, etc., 

 which are green in darkness, spring from 

 seeds not covered by opaque coats while they 

 are ripening. Thus we do not know that seeds 

 of pine, for example, if made to mature in 

 darkness on the tree, would not yield as color- 

 less seedlings as those of Gingho, Welwitschia 

 and the other " living fossils " if similarly 

 sprouted in the dark. 



The nest chapter is on the autumn yellow- 

 ing of leaves. Here are recorded or quoted 

 analyses indicating the differences in the con- 

 tent of leaves before and after the autumn 

 change takes place. Thus in equal pieces of 

 the same leaves cut out (by cork-borer) before 

 and after yellowing there is found to be little 

 change in the proportions of magnesium, an 

 increase in calcium, sodium and sulphur, a 

 decrease to one half in nitrogen, phosphorus, 

 potassium, iron, chlorine and silica. The 

 significance of these facts is thus interpreted: 

 the yellow constituents of chlorophyll are 

 composed of elements which are abundant and 

 easily obtained, whereas the green pigments 

 consist of less abundant elements less easily 

 obtained; so, in yellowing or in etiolated 

 parts, the green is withdrawn or is not 

 formed, and there is a corresponding economy. 

 Whether one will agree with this conclusion 

 or will dissent from it will depend upon 

 whether one has, as Stahl himself points out, 

 the ecological or the physiological jvoint of 

 view. 



Stahl's paper on chlorophyll is a valuable 

 contribution to the subject. It contains many 



references to the abundant literature; it sug- 

 gests both further reflection and more work 

 in the laboratory. It is stimulating, perhaps 

 more so because it is not convincing. 



George J. Peirce 

 Stanfobd Univeesitt, Callfobnia 



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