776 SUMMAKV OF CURRENT RESEARCHES RELATING TO 



Physiology. 

 Nutrition and Growth. 



Opinions upon Physiology of Leaf-fall.* — R. Combes publishes a 

 paper dealing with the opinion, held by Sachs and others, that substance- 

 contained in falling leaves are useless to the plant. The writer refers to 

 the influence which this opinion has had upon deductions made from 

 microchemical researches, and then discusses the variations produced in 

 autumn, in the mineral substances, nitrogenous compounds and hydro- 

 carbons contained in leaves. Finally he concludes that there is no proof 

 that the substances useful to living plants are transferred from the 

 leaves to the stem during the period of leaf -fall. It appears necessary 

 to make more exact experiments at very frequent intervals upon leaves 

 before, during, and after fall ; these experiments should be made with 

 leaves exposed to ordinary atmospheric conditions and upon those pro- 

 tected from rain, etc., while simultaneous experiments should be made 

 upon living parts of the plant. The chemical composition of leaf -con- 

 tents should also be analysed at different stages. The loss or accumula- 

 tion of substances in falling leaves varies according to species, atmospheric 

 conditions, first frosts, etc. Chemical composition is modified in a 

 similar way ; thus frost causes increase in oxidation and hence an accu- 

 mulation of substances rich in oxygen ; likewise starch is transformed 

 into sugar under the influence of frost. Since it has been proved that 

 such substances as sugar and amides can accumulate in falling leaves, 

 the author regards Sachs' opinion as quite inadmissible, and contends 

 that chemical change, persistence, accumulation, or diminution of sub- 

 stances contained in falling leaves, can no longer be regarded as explaining 

 the physiological role of these substances. 



Complementary Chromatic Adaptation in Plants.f — P. A. Dangeard 

 has investigated this phenomenon in the Cyanophycea? by means of a 

 special spectrograph, and finds that the normal colours of the alga? are 

 preserved when exposed to that part of the spectrum which has no effect 

 upon the growth, i.e. from the violet to the yellow 7 rays. They become 

 green under the rays extending from the yellow to the infra-red. The 

 rays which are the most active in chlorophyll-synthesis are those which 

 determine the change in coloration. 



Irritability. 



Effect of Etherization on Metabolism. } — J. Hempel has studied 

 the effects of anaesthetics such as ether upon the seeds and seedlings of 

 Pisum and Lupimis, and also upon the buds of Acer Psmdoplatanus, and 

 potato-tubers. The writer finds that small doses of ether accelerate the 

 production of CO.,, especially at low temperatures, while large doses 

 retard it in proportion to the size of the doses. During the after-effect 

 there is no acceleration, but the respiratory process is retarded both by 



* Rev. Gen. Bot., xxiii. (1911) pp. 129-64. 

 t Comptes Rendus, cliii. (1911) pp. 293-4. 



X Mem. Acad. Rov. Sc. and Lett. Danemark, Copenhagen, ser. 7, vi. (1911) 

 pp. 215-78. 



