294 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



Migration of Mineral Substances from Dying Leaves. By E. 



Ramann (Landwirtsch. Versuchsstat. lxxvi. 157-168 ; 1912). — The 

 author continues, in two papers on this subject, the interesting series 

 of studies on the metabolism of deciduous trees which he has carried 

 on for several years, both independently and in conjunction with 

 H. Bauer. The first paper deals with the migration of mineral sub- 

 stances from leaves during the normal process of autumnal fall, the 

 second with the migration occurring in leaves killed by frost. During 

 spring and summer large quantities of mineral matter accumulate in 

 the leaves, owing to the transpiration process, while in autumn there 

 is a migration of mineral matter from the leaves to other parts of the 

 plant prior to the cutting-off of the leaf by the absciss layer. Ash 

 analyses show that in the comparatively short interval that elapses 

 between the assumption of the autumn colouring, owing to changes 

 in the chlorophyll of the dying cells, and the actual death of the leaf, 

 there is a rapid passage of nitrogenous compounds, potassium salts, 

 and phosphates from leaf to stem. But, on the other hand, calcium 

 salts and silica increase in amount in the dying leaf, and the amount 

 of these substances may be twice as great as in normal green leaves. 

 The results of Ramann's analyses of the leaves of various trees are 

 of considerable horticultural and ecological interest ; for instance, 

 the well-known fact that beech and oak make rich humus is evidently 

 connected with the fact tnat their leaves retain an unusually large 

 proportion of their nitrogenous and phosphorus-containing compounds. 



In the second paper, Ramann gives the results of analyses of pear 

 leaves, some of which were killed by frost, while others remained 

 uninjured. The former showed diminution in potassium and phos- 

 phorus, but increase in calcium content, exactly as in normal autumn 

 withering, though the migration of substances from the leaf was less 

 marked. Migration of substances into and out of the leaf took place 

 during the short period between the thawing and the perishing of the 

 frozen leaves ; but since death of the tissues in non-resistant leaves 

 like those of pear takes place during the actual freezing, and not after 

 thawing, the exit of the potash and phosphoric acid would be simply 

 a post-mortem change due to osmotic diffusion, and could not therefore 

 be effected in a period too short to allow of the conversion and transport 

 of organic nitrogenous substances. — F. C. 



Milkweed. By Arthur C. Neish, Ph.D. (Jour. Soc. Chem. Ind., 

 vol. xxii. No. 2, pp. 72-73). — An investigation to ascertain whether the 

 various milkweeds of America, which abound in such quantity, could 

 not be made use of. Asclepias incarnata and others were taken 

 in hand. Two to three per cent, of rubber had been previously 

 shown by another author to be present in the latex, but both quantity 

 and quality are such as to render this of little commercial interest. 

 The stalk yielded fibre up to 6 feet in length closely resembling flax, 

 but stronger, white, and of silky appearance, which should be of value 

 for textile or rope manufacture. The dried seeds yielded over 20 per 



