LrrTNBAN SOCIETY OF LONDON. 1 5 



of chlorophyll and copper. Of the various stains carmine proved 

 to be the most generally useful, in the form of Carmalum or 

 Alum-carmine. A water solution of 1 in 50 or 1 in 100 was 

 generally adopted. It soon loses its stainiiig power as one speci- 

 men after another is dipped, and this gives scope for grading the 

 colour. Immersion varies from about 10 minutes to 2 hours, 

 according to the strength of the solution. HaBmalum may be 

 used for red algae that have a purple tone, in connection with 

 Congo-red or carmalum, each stain being used independently. 

 Carmalum is the most durable stain ; specimens placed in formalin 

 and kept on a shelf in subdued light have not materially de- 

 colorised in 4^ years. For brown algae, notably for Fucus and 

 allied genera, fixing in picric acid is often better than treatment 

 with copper-acetate. Ascophyllum turns to a pleasing green in 

 copper-acetate ; in such a case and where dried specimens such as 

 Laminaria have too green a colour, it is generally possible to pro- 

 duce a brown tone by immersing in a solution of permanganate of 

 potash. 



Thes(i experiments have been carried out in connection with 

 the exhibition of plants in the Depai'tment of Botanv, Natural 

 History Museum, S. Kensington, where specimens can be seen. 



A discussion followed in which the participants were : — 

 Lt.-Col. Tull Walsh, Dr. O. Stapf, Dr. A. B. Eendle, Mr. H. W. 

 Darlington, and Mr. A. H. Maude, the author repljang. 



Dr. E. E. Gates, T.L.S., read his paper " A Systematic Study 

 of the North American Melanthacere from the Genetic Stand- 

 point," which was illustrated by a series of .31 photographs taken 

 from the herbarium specimens, and by examples from the Linnean 

 and Smithiau herbaria belonging to the Society. 



The author's point of view is the assumption, based upon 

 experiment during the last fifteen years, that the variations wdiich 

 mark species have not been universally continuous and infi- 

 nitesimal, but often definite and discontinuous. Definite variation 

 is not necessarily orthogenetic variation, but marked variation 

 which may occur in any, or in many, directions simultaneously. 

 The experience gained in work on the mutations in (Enothera are 

 turned to account in this group of Liliales which has not hitherto 

 been the subject of experiment. 



Pairs of species have been taken and investigated on this basis. 

 Eelated genera showing marked differences in structure often co- 

 exist side by side, showing that these differences cannot be claimed 

 as of selective value, but have arisen from " spontaneous variation " 

 and have been perpetuated by heredity. 



The photographs illustrating the reading of the paper were 

 taken from the Herbarium of the University of California. 



The paper was discussed by Dr. Ethel N. Thomas, Dr. 0. Stapf, 

 a,nd Dr. A. B. Eendle, the author replying. 



